|C^W^^\ 


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A  TEXT-BOOK 


OF 


HISTOLOGY 

INCLUDING  MICROSCOPIC  TECHNIC 

BY 

A.   A.   BÖHM,  M.  D,,  and  M.  VON   DAVIDOFF,  M.  D. 

of  the  Anatomical  Institute  in  Munich 

Edited,  with  Extensive  Additions  to  both  Text  and   Illustrations 


G.  CARL  HUBER,  M.D. 

Professor  of  Histology  and  Embryology  and  Director  of  the  Histological  Laboratory, 

University  of  Michigan,  Ann  Arbor;  Professor  of  Embryology, 

Wistar  Institute  of  Anatomy,  Philadelphia 


Second  Edition 
Thoroughly  Revised  and  Enlargfed 


WITH  377  ILLUSTRATIONS 


PHILADELPHIA  AND  LONDON 

W.  B.  SAUNDERS    COMPANY 

J9U 


Copyright,   1900,   by    W.  B.  Saunders  and  Company.      Reprinted  July,   1901. 

Revised,  reprinted,  and  recopyrighted  August,  1904.       Reprinted 

April,   1905,   January,    1906,  July,  1908,  June,   1909, 

October,  1909,  and  September,  1910. 


Copyright,  1904,  by  W.  B.  Saunders  &  Company. 


Registered  at  Stationers'  Hall,  London,  England. 


Reprinted  July,  1911. 


PRINTED     IN    AMERICA 


PRESS    OF 

W.    B.    SAUNDERS    COMPANY 

PHILADELPHIA 


TO  THEIR  TEAC2iER 

PROFESSOR   C  VON  KUPFFER 

THIS  BOOK  IS  DEDICATED  BY 

THE  GRATEFUL  AUTHORS 


EDITOR'S    PREFACE    TO    THE    SECOND 

EDITION. 


The  favorable  reception  accorded  to  the  first  American  edition  of 
Böhm  and  Davidoff 's  Text-book  of  Histology  has  justified  the  as- 
sumption expressed  by  the  editor  in  his  preface  to  the  former  edition, 
that  an  English  translation  of  this  work  would  meet  with  approval 
from  American  and  EngHsh  teachers  and  students. 

In  the  preparation  of  this  second  American  edition  the  editor 
has  retained  in  general  the  same  arrangement  of  the  subject-matter 
as  presented  in  the  former  edition.  The  revision  of  the  text  has 
given  opportunitv  to  take  cognizance  of  the  many  contributions  to 
our  knowledge  of  the  ultimate  structure  of  tissues  and  organs  and 
of  their  histogenesis  which  have  appeared  in  recent  years,  and  in 
doing  so,  many  of  the  chapters,  especially  those  dealing  with  gen- 
eral liistology,  have  been  subjected  to  extensive  alterations.  Re- 
cognition ha^'s  also  been  given  to  the  results  obtained  by  the  use  of 
precise  methods  of  plastic  reproduction,  methods  which  have  been 
especially  useful  in  giving  clearer  and  more  accurate  conceptions  of 
the  form  and  relationship  of  anatomic  structures,  too  small  and  too 
delicate  to  admit  of  disassociation  by  means  of  methods  of  macera- 
tion and  teasing  and  too  complicated  to  admit  of  full  interpretation 
by  means  of  sections.  Maziarski's  observations  on  the  form  and 
relationship  of  the  ultimate  divisions  of  the  tubular  systems  of  many 
of  the  more  important  glands  have  been  embodied,  also  the  results 
of  numerous  reconstructions  made  in  the  Histological  Laboratory 
of  the  University  of  Michigan. 

The  text  of  this  edition  has  been  extended  by  some  forty  pages, 
and  the  illustrations  have  been  increased  from  three  hundred  and 
fiftv-one  to  three  hundred  and  seventy-seven.  Recognizing  the 
fact  that  a  text-book  of  Histology  is  a  book  which  of  necessity 
needs  to  be  ccnistantly  used  in  the  laboratory,  and  its  size  is, 
therefore,  a  matter  of  some  importance,  the  editor  seemed  justi- 
fied, in  view  of  the  fact  that  an  increase  in  the  number  of  text-pages 
seemed  inevitable,  to  dispense  in  the  present  edition  with  the  list  of 
references  to  the  literature  (some  twenty  pages)  which  appeared  in 

the  former  edition. 

G.  Carl  Huber. 

Laboratory  of  Histology  and  Embryology, 
University  of  Michigan. 


EDITOR'S   PREFACE   TO  THE   FIRST 
EDITION. 


The  "  Text -book  of  Histology  "  by  Böhm  and  v.  Davidoff,  as  stated 
t>Y  the  authors  in  the  preface  to  the  first  edition,  presents  as  fully  as 
possible,  from  both  the  theoretic  and  technical  standpoints,  the  subject- 
matter  of  the  lectures  and  courses  in  histology  given  to  students  in  the 
University  of  Munich.  The  authors  further  state  that  in  the  completion 
of  their  work  they  had  the  constant  aid  and  advice  of  Professor  von 
Kupffer,  and  had  at  their  disposal  the  sections  in  the  collection  of  the 
histologic  laboratory  in  Munich,  which  were  freely  used  in  the  selection 
and  preparation  of  the  illustrations  accompanying  the  text. 

The  excellence  of  the  text  and  illustrations  of  the  German  edition, 
attested  by  all  familiar  with  the  Avork,  and  the  cordial  reception  which  it 
has  received  from  both  students  and  investigators,  justify  the  belief  that 
an  English  translation  will  meet  with  approval  from  American  and 
English  teachers  and  students. 

In  the  preparation  of  this  American  edition  the  editor  has  retained 
substantially  all  the  subject-matter  and  illustrations  of  the  second  German 
edition,  although  certain  minor  changes  in  the  arrangement  of  the  text 
seemed  desirable.  Additions  to  the  German  text  have  been  freely  made. 
The  sections  on  the  Motor  and  Sensory  Nerve -endings  and  on  the  Spinal 
and  Sympathetic  Ganglia  have  been  greatly  expanded,  and  the  Innerva- 
tion of  Glands  and  Organs  has  been  considered  much  more  fully  than  in 
the  original.  Our  knowledge  of  the  normal  function  of  tissues  and 
organs  is  so  dependent  on  a  correct  understanding  of  their  innervation 
that  this  subject  seemed  deserving  of  fuller  consideration  than  is  generally 
given  it  in  text-books  of  this  scope.  The  glands  with  internal  secretion 
have  also  been  considered  more  fully  than  in  the  original  text,  their  im- 
portance necessitating  such  treatment.  More  than  one  hundred  illustra- 
tions, the  majority  of  them  from  original  drawings,  have  also  been  added. 
In  making  these  and  other  minor  additions  the  editor  has  striven  to 
stamp  his  own  work  with  the  excellent  features  of  the  German  text,  and 
trusts  that  his  endeavors  may  have  added  to  the  usefulness  of  the  book. 

The  editor  acknowledges  with  pleasure  his  indebtedness  to  Dr. 
Herbert  H.  Gushing  for  his  excellent  and  accurate  translation,  and  for 
suggestions  received  from  him.  The  publishers,  Messrs.  Saunders  & 
Company,  have  shown  throughout  the  greatest  interest  in  the  work,  and 
deserve  the  gratitude  of  the  editor  for  their  ready  acquiescence  in  all 
suggestions  made  by  him,  for  the  excellent  reproduction  of  his  drawings, 
and  for  the  suggestions  made  to  him.  The  editor  is  particularly  in- 
debted to  his  able  assistant,  Dr.  Lydia  M.  De  Witt,  for  valuable  assistance 
rendered,  more  especially  in  the  tedious  work  of  proof-correction,  for 
which  he  expresses  his  sincere  appreciation  and  gratitude. 

G.  Carl  Huber. 

University  of  Michigan,  Ann  Arbor,  Mich. 


CONTENTS. 


INTRODUCTION  TO  MICROSCOPIC  TECHNIC 


PAGE 


Microscope  and  Its  Accessories '7 

Microscopic  Preparations           ^^ 

Methods  of  Maceration ^^ 

Fixing  Methods ^3 

Infiltration  and  Imbedding ^7 

Paraffin • ^7 

Celloidin 3° 

Celloidin-Paraffin 32 

Microtomes  and  Sectioning 3^ 

Further  Treatment  of  the  Section 3° 

Fixation  to  the  Slide  and  Removal  of  Paraffin 3° 

Staining ^ 

Section  Staining 4 

Staining  in  Bulk 40 

Methods  of  Impregnation 47 

Preparation  of  Permanent  Specimens 5 2 

Methods  of  Injection     .    .            53 

Reconstruction  by  Means  of  Wax  Plates 55 


GENERAL  HISTOLOGY. 
L  THE  CELL. 


59 


Cell-body y 

Nucleus ■ 

Nuclear  and  Cell-division ^4 

Mitosis  or  Karyokinesis  (Indirect  Cell-division) 04 

Prophases °° 

Metaphases ^^ 

Anaphases "9 

Telophases 7° 

Heterotypic  Form  of  Mitosis 7° 

Amitosis  7° 

Process  of  Fertilization       71 

Chromatolysis 74 

Technic  for  the  Cell      74 

n.  TISSUES. 

Epithelial  Tissues ^° 

Simple  Epithelium     ....  °2 

Simple  Squamous  Epithelium • °^ 

Simple  Cubic  Epithelium      °2 

Simple  Columnar  Epithelium °3 

Pseudostratified  Columnar  Epithelium         oj 

Stratified  Epithelium °3 

Stratified  Squamous  Epithelium «4 

Transitional  Epithelium °5 

Stratified  Columnar  Epithelium *5 


ö  CONTENTS, 

PAGE 

Glandular  Epithelium 87 

Unicellular  Glands 87 

Multicellular  Glands 88 

General  Consideration  of  the  Structure  and  Classification  of  Glands  ...  88 

Tubular  Glands      89 

Alveolar  Glands     .... 91 

Remarks  on  the  Process  of  Secretion 92 

Neuro-epithelium 92 

Mesothelium  and  Endothelium 92 

Technic  for  Epithelial  Tissues 94 

Connective  Tissues 96 

Mucous  Connective  Tissue 1 00 

Reticular  Connective  Tissue , 100 

Fibrous  Connective  Tissue loi 

Adipose  Tissue 107 

Cartilage I08 

Bone 112 

Structure  of  Bone       II2 

Development  of  Bone 116 

Technic  for  Connective  Tissues 126 

Muscular  Tissues    .    , 134 

Nonstriated  Muscle-cells 134 

Striped  Muscle-fibers 136 

Development  of  Voluntary  Muscle-fibers 144 

Cardiac  Muscle 145 

Technic  for  Muscular  Tissue 147 

Nervous  Tissues 148 

Nerve-cells  or  Ganglion  Cells  ;   Cell-bodies  of  Neurones I49 

Nerve-fibers 157 

Peripheral  Nerve  Terminations ■. 162 

Technic  for  Nervous  Tissues .'    .    .    .  180 


SPECIAL  HISTOLOGY. 

I.  BLOOD  AND  BLOOD-FORMING   ORGANS,  HEART, 
BLOOD-VESSELS,  AND   LYMPH- VESSELS. 

Blood  and  Lymph 186 

Formation  of  Blood ,    .    .  186 

Red  Blood-corpuscles 187 

White  Blood-corpuscles         .    .  ■ 191 

Blood  Platelets — Thrombocytes 194 

Behavior  of  Blood-cells  in  the  Blood  Current 196 

Lymphoid  Tissue,  Lymph-nodules,  and  Lymph-glands I96 

Spleen 202 

Bone-marrow      .    .    .    , 207 

Thj'mus  Gland 210 

n.  CIRCULATORY  SYSTEM, 

Vascular  System 213 

Heart' 213 

Blood-vessels 216 

Arteries •     ...  216 

Veins   . 219 

Capillaries 220 

Anastomoses,  Retia  Mirabilia,  and  Sinuses 222 

Lymphatic  System 223 

Lymph-vessels 223 

Lymph-capillaries,  Lymph-spaces,  and  Serous  Cavities  224 

Carotid  Gland  (Glandula  Carotica,  Glomus  Caroticum) 225 

Technic  for  Blood  and  Blood-forming  Organs 226 

Technic   for  Circulatory  System 235 


CONTENTS.  9 

UL  DIGESTIVE  ORGANS. 

Oral  Cavity 235 

Teeth 238 

Structure  of  the  Adult  Tooth , 238 

Development  of  the  Teeth 243 

Tongue 247 

Lingual  Mucous  Membrane  and  Its  Papillse .  247 

Taste-buds 249 

Lymph-follicles  of  the  Tongue  (Folliculi  Linguales)  and  the  Tonsils  ...  251 

Pharyngeal  Tonsil 251 

Glands  of  the  Oral  Cavity 253 

Salivary  Glands 255 

Parotid  Gland  (Serous  Gland) 255 

Sublingual  Gland  (Mucous  Gland)      255 

Submaxillary  Gland  (Mi.xed  Gland) ; 258 

Small  Glands  of 'the  Mouth 259 

Pharynx  and  Esophagus 262 

Stomach  and  Intestines 264 

General  Structure  of  the  Intestinal  Mucous  Membrane 264 

Stomach       266 

Small  Intestine 274 

Large  Intesdne,  Rectum,  and  Anus    ...                 2-8i 

Blood,  Lymph,  and  Nerve  Supply  of  the  Intestine 283 

Secretion' of  the  Intestine  and  the  Absorption  of  Fat 288 

Liver 289 

Pancreas      298 

Technic  for  Digestive  Organs 303 

IV.  ORGANS  OF  RESPIRATION. 

Larynx 3°9 

Trachea 310 

Bronchi,  their  Branches,  and  the  Bronchioles              31 1 

Terminal  Divisions  of  Bronchi  and  Ultimate  Air-spaces    , 313 

Thyroid  Gland 319 

Parathyroid  Glands 321 

Technic  for  Organs  of  Respiration 322 

V.  GENITO-URINARY  ORGANS. 

Urinaiy  Organs 323 

Kidney 323 

Pelvis  of  the  Kidney,  Ureter,  and  Bladder 336 

Suprarenal  Glands      .    .         .         339 

Technic  for  Urinary  Organs  and  Suprarenal  Body 342 

Female  Genital  Organs 344 

Ovum 344 

Ovary       344 

Fallopian  Tubes,  Uterus,  and  Vagina              ....  354 

Male  Genital  Organs 361 

Spermatozoon 3^'' 

Testes 362 

Excretory  Ducts 367 

Spermatogenesis 372 

Technic  for  Reproductive  Organs • 378 

VL  THE  SKIN  AND  ITS  APPENDAGES. 

Skin  (Cutis) 379 

Hair 389 

Nails • 394 

Glands  of  the  Skin 396 

Sweat-glands      . .  39^ 

Sebaceous  Glands 39^ 

Mammary  Glands       .             400 

Technic  for  the  Skin  and  Its  Appendages 403 


lO  CONTENTS. 

Vn.  THE  CENTRAL  NERVOUS  SYSTEM. 

Spinal  Cord 406 

Cerebellar  Cortex 413 

Cerebral  Cortex 416 

Olfactory  Bulb 421 

Epiphysis  and  Hypophysis 422 

Ganglia 424 

General  Survey  of  the  Relations  of  the  Neurones  to  One  Another  in  the  Central 

Nervous  System 431 

Neuroglia 434 

Membranes  of  the  Central  Nervous  System 436 

Blood-vessels  of  the  Central  Nervous  System 439 

Technic  for  Central  Nervous  System 440 

VIIL  EYE. 

General  Structure 446 

Development  of  the  Eye 446 

Tunica  Fibrosa  Oculi 448 

Sclera       448 

Cornea 449 

Vascular  Tunic  of  the  Eye    .    . 452 

Choroid,  Ciliary  Body,  and  Iris 452 

Internal  or  Nervous  Tunic  of  the  Eye 457 

Pigment  Layer 457 

Retina      ....             457 

Region  of  the  Optic  Papilla 460 

Region  of  the  Macula  Lutea 460 

Ora  Serrata,  Pars  Ciliaris  Retinge,  and  Pars  Iridica  Retinae 461 

Miiller's  Fibers  of  the  Retina 462 

Relations  of  the  Elements  of  the  Retina  to  One  Another 462 

Optic  Nerve 464 

Blood-vessels  of  the  Optic  Nerve  and  Retina 465 

Vitreous  Body             467 

Crystalline  Lens                  467 

Fetal  Blood-vessels  of  the  Eye 468 

Interchange  of  Fluids  in  the  Eyeball  . 469 

Protective  Organs  of  the  Eye , 469 

Lids  and  Conjunctiva 469 

Lacrimal  Apparatus 473 

Technic  for  the  Eye 474 

IX.  ORGAN  OF  HEARING. 

External  Ear 476 

Middle  Ear 478 

Internal   Ear 480 

Utriculus  and  Sacculus      482 

Semicircular  Canals 483 

Cochlea       .             484 

Organ  of  Corti         .                  489 

Development  of  the  Labyrinth 496 

Technic  for  Organ  of  Hearing 497 

X.  ORGAN  OF  SMELL. 

Technic  for  Nasal  Mucous  Membrane 500 

XI.  GENERAL  CONSIDERATIONS  OF  THE  SPECIAL 
SENSE-ORGANS. 


Index 501 


ILLUSTRATIONS. 


FIG.  PAGE 

1.  Microscope      ...             l8 

2.  Diagram  showing  the  principle  of  a  compound  microscope  .         20 

3.  Box  for  imbedding  tissues          28 

4.  Laboratory  microtome ^;^ 

5.  Minot  automatic  precision  microtome 34 

6.  Minot  automatic  rotary  microtome 34 

7.  Apparatus  for  cutting  tissues  frozen  by  carbon  dioxid 37 

8.  Movements  in  honing 38 

9.  Apparatus  for  making  wax  plates,  used  in  reconstruction  by  Bern's  method  .    .  56 

10.  Diagram  of  cell  (Huber) 59 

11.  Cylindric  ciliated  cells  from  the  primitive  kidney  of  /'(?^'r(7;«jj'3(?«//a«ifr2     ...  60 

12-26.    Processes  of  mitotic  cell-  and  nuclear  division 65,  66 

27-29.   Mitotic  cell-division  of  fertilized  whitefish  eggs  (Huber) 67 

30.    Mitotic  division  of  cells  in  testis  of  salamander  (Benda  and  Guenther)      ...  69 

31-36.    Process  of  fertilization  (Boveri)      .  72,  73 

37.  Pigment  cell  from  the  skin  of  the  head  of  a  pike 77 

38.  Isolated  cells  of  squamous  epithelium  (Huber)      82 

39.  Surface  view  of  squamous  epithelium  from  skin  of  a  frog                  82 

40.  Simple  columnar  epithelium  from  the  small  intestine  of  man  (Huber)  ....  83 

41.  Pseudostratified  columnar  epithelium 83 

42.  Stratified  pavement  epithelium           .    .             .    .  84 

43.  Cross-section  of  stratified  squamous  epithelium  from  esophagus  of  man  (Huber)  84 

44.  Isolated  transitional  epithelial  cells  from  bladder  of  man  (Huber)          ....  85 

45.  Cross-section  of  transitional  epithelium  from  the  bladder  of  a  young  child  (Huber)  85 

46.  Stratified  columnar  epithelium       86 

47.  Ciliated  cells  from  bronchus  of  dog          ...         86 

48.  Cross-section  of  stratified   ciliated   columnar  epithelium  from  trachea  of  rabbit 

(Huber)      86 

49.  Goblet  cells  from  bronchus  of  dog        87 

50.  Mucus-secreting  cell  (goblet  cell)  (Huber) 87 

51.  Simple  tubular  glands 88 

52.  Excretory  ducts  and    lumina  of  the  secretory   portion  of  a  compound  tubular 

gland  .         , 89 

53.  Lumina  of  the  secreting  portion  of  a  reticulated  tubular  gland 89 

54.  Glandular  classification       ....                 90 

55-    Mesothelium  from  pericardium  of  rabbit  (Huber) 93 

56.  Mesothelium  from  mesentary  of  rabbit  (Huber) 93 

57.  Mesothelium  from  peritoneum  of  frog 93 

58.  Mesothelium  covering  posterior  abdominal  wall  of  frog  (Huber) 94 

59.  Endothelial  cells  from  small  artery  of  mesentery  of  rabbit  (Huber) 94 

60.  Mesenchymatous  tissue  from  the  subcutis  of  a  duck  embryo 97 

61.  Development  of  the  different  types  of  connective  tissue  from  the  mesenchvma 

(Huber) '.  98 

62.  White  fibrils  and  bundles  from  teased  preparation  of  a  fresh  tendon  from  tail  of 

rat  (Huber) 99 

62^.    Elastic  fibers  from  ligamentum  nuchae  of  ox 99 

63.  Reticular  fibers  from  a  thin  section  of  a  lymph-gland  (Huber) loi 

64.  Reticular  connective  tissue  from  lymph-gland  of  man  ...         102 

65.  Areolar  connective  tissue  from  subcutaneous  tissue  of  rat  (Huber) 102 

66.  Cell-spaces  in  the  ground- substance  of  areolar  connective  tissue  of  young  rat 

(Huber)          103 

67.  Connective-tissue  cells  from  pia  mater  of  dog  (Huber) 103 

68.  Pigment  cells  found  on  the  capsule  of  sympathetic  ganglion  of  frog  (Huber)  .  103 

69.  Leucocyte  of  frog  with  pseudopodia 104 

70.  Fibrous  connective  tissue  from  great  omentum  of  rabbit 105 

II 


12  ILLUSTRATIONS. 

FIG.  PACK 

71.  Longitudinal  section  of  tendon 106 

72.  Cross-section  of  secondary  tendon  bundle  from  tail  of  rat  (Huber) 106 

73.  Tendon  cells  from  tail  of  rat  (Huber) 107 

74.  Cross- sectioi:i  of  ligamentum  nuchpe  of  ox  (Huber) 107 

75.  Fat-cell 107 

76.  Hyaline  cartilage 108 

77.  Section  through  cranial  cartilage  of  squid 109 

78.  Insertion  of  the  ligamentum  teres  into  the  head  of  the  femur     .......  no 

79.  Elastic  cartilage  from  external  ear  of  man in 

80.  Longitudinal  section  through  a  lamellar  system  (v.  Ebner) 113 

81.  82.    Lamellae  seen  from  the  surface  (v.  Ebner)                   113 

^3-    Segment  of    a  transversely  ground  section    from    the  shaft  of  a  long  bone, 

showing  lamellar  system ...  1 14 

84.  Portion  of  a  transversely  ground  disc  from  the  shaft  of  a  human  femur    ...  115 

85.  Longitudinal  section  through  a  long  bone  of  a  lizard  embryo        ......  1 17 

86.  Longitudinal  section  of  the  proximal  end  of  a  long  bone  of  a  sheep  embryo  .  118 

87.  Longitudinal  section  through  area  of  ossification  from  long  bone  of  human 

embryo  (Huber)     ...         .             ......  119 

88.  Longitudinal  section  through  epiphysis  of  arm  bone  of  sheep  embryo  ....  122 

89.  Section  through  the  lower  jaw  of  an  embryo  sheep 123 

90.  Cross-section  of  developing  bone  frorn  leg  of  human  embryo,  showing  endo- 

chondral and  intramembranous  bone  development  (Huber)      .    .             ...  124 

91.  Cross-section  of  shaft  (tibia  of  sheep) 125 

92.  Nonstriated  muscle  from  the  intestine  of  a  cat 135 

93.  Cross-section  of  striated  muscle-fibers 136 

94.  Muscle-fiber  from  ocular  muscles  of  rabbit 136 

95.  Striated  muscle-fiber  of  frog,  showing  sarcolemma  (Huber) 137 

96.  Diagram  of  structure  of  fibrils  of  a  striated  muscle-fiber  (Huber) 138 

97.  Diagram  of  transverse  striation  in  the  muscle  of  an  anthropoid 138 

98.  Transverse  section  through  the  striated  muscle-fiber  of  a  rabbit 139 

99.  Striated  muscle-fiber  of  man 140 

100.   Cross-section  througlj  the  trapezius  muscle  of  man 140 

loi.    Branched,  striated  muscle-fiber  from  tongue  of  dog  (Huber) 141 

102.  Cross-section  of  rectus  abdominis  of  child,  under  low  magnification  (Huber)  142 

103.  Longitudinal  section  through  the  line  of  junction  between  muscle  and  tendon  142 

104.  105.    Longitudinal  and  cross-section  of  muscle-fibers  from  the  human  myocar- 

dium      143 

106.  Longitudinal  section  of  heart-muscle  (Huber) 146 

107.  Bipolar  ganglion  cell  from  the  ganglion  acusticum  of  a  telecost 150 

108.  Chroniatophile  granules  of  a  ganglion  cell  from  the  Gasserian  ganglion  of  a 

telecost 151 

109.  Nerve-cell  from  the  anterior  horn  of  the  spinal  cord  of  an  ox 151 

no.    Motor    neurones    from   anterior    horn  of    the   spinal    cord  of   new-born    cat 

(Huber) 152 

111.  A  nerve-cell  with  branched  dendrites  (Purkinje's  cell),  from  cerebellar  cortex 

of  rabbit              152 

112.  Pyramidal  cell  from  cerebral  cortex  of  man               153 

113.  Nerve-cell  from  dendrites  ending  in  claw-like  telodendria 154 

114.  Ganglion  cell  with  a  T-shaped  process 154 

115.  Ganglion  cell  from  Gasserian  ganglion  of  rabbit  (Huber) 155 

116.  Ganglion  cells  from  spinal  ganglion  of  rabbit  embryo 155 

117.  Neurone  from  inferior  cervical  sympathetic  ganglion  of  rabbit  (Huber)  .    .    .  156 

118.  Longitudinal  section  of  nerve-fiber    . 157 

119.  Transverse  section  through  sciatic  nerve  of  frog 158 

120.  Medullated  nerve-fibers  from  rabbit 159 

121.  Remak's  fibers  from  pneumogastric  nerves  of  rabbit 159 

122.  Diagram  to  show  composition  of  a  peripheral  nerve-trunk  (Huber)      ....  161 

123.  Cross-section  through  a  peripheral  nerve 161 

124.  Peripheral  motor  neurone  (Huber) 163 

125.  Motor  nerve-ending  in  voluntary  muscle  of  rabbit  (Huber-De  Witt)  ....  164 
126-130.    Motor  endings  in  striated  voluntary  muscles 165 

131.  Motor  nerve-ending  in  striated  voluntary  muscle  of  frog  (Huber-De  Witt)   .    .  166 

132.  Motor  nerve-ending  on  heart  muscle-cells  of  cat  (Huber-De  Witt)      ....  166 

133.  Motor  nerve-ending  on  involuntary  nonstriated  muscle-cell  from  intestine  of 

cat  (Huber-De  Witt) 166 


ILLUSTRATIONS.  1 3 

FIG  PAGE 

134.  Peripheral  sensory  neurone  (Huber) 167 

135.  Termination  of  sensory  nerve-fibers  in  the  mucosa  and  epithelium  of  urethra 

of  cat  (Huber) 168 

136.  End-bulb  of  Krause  from  conjunctiva  of  man  (Dogiel) 169 

137.  Meissner' s  tactile  corpuscle  (Dogiel)    .    .             170 

138.  Genital  corpuscle  from  glans  penis  of  man  (Dogiel) 171 

139.  Cylindric  end-bulb  of  Krause  from  intermuscular  fibrous  tissue  septum  of  cat 

(Huber) 172 

140.  Vater- Pacinian  corpuscle  from  the  mesentery  of  a  cat 173 

141.  Pacinian  corpuscles  from  the  mesorectum  of  a  kitten  (Sala) 174 

142.  Corpuscle  of  Herbst  from  bill  of  duck 175 

143.  Intrafusal  muscle-fiber  from  neuromuscular  nerve  end-organ  of  rabbit  (Huber)  176 

144.  Cross-section  of  a  neuromuscular  nerve  end-organ  from  interosseous  muscle  of 

man  (Huber) ...  176 

145.  Neuromuscular  nerve  end-organ  from  plantar  muscles  of  dog  (Huber-De  Witt)  177 

146.  Neurotendinous  nerve  end-organ  from  rabbit  (Huber-De  Witt) 178 

147.  Cross-section  of  neurotendinous  nerve  end-organ  of  rabbit  (Huber-De  Witt)  .  179 

148.  Ranvier's  crosses  from  sciatic  nerve  of  rabbit       181 

149.  Medullated  nerve-fiber  from  sciatic  nerve  of  frog 181 

150.  Ganglion  cell  from  anterior  horn  of  spinal  cord  of  calf 182 

151.  Human  red  blood-cells 188 

152.  Rouleau  formation  of  human  erythrocytes 188 

153.  Hemin,  or  Teichmann's  crystals,  from  blood  stains  on  a  cloth  (Huber)  .    .    .  188 

154.  Crenated  human  red  blood-cells 188 

155.  Red  blood-corpuscles  subjected  to  the  action  of  water 188 

156.  Red  blood-corpuscles  from  various  vertebrate  animals 189 

157.  White  blood-corpuscles  from  normal  blood  of  man 191 

158.  Ehrlich's  leucocytic  granules       192 

159.  Fibrin  from  laryngeal  vessel  of  child  (Huber) 195 

160.  Solitary  lymph-nodule  from  human  colon 197 

161.  Transverse  section  of  human  cervical  lymph-gland,  showing  the  general  struc- 

ture of  a  lymph-gland  ...         .  198 

162.  Section  from  human  lymph-gland 199 

163.  Section  through  the  human  spleen 203 

164.  Lobule  of  the  spleen  (Mall)       205 

165.  Cells  containing  pigment,  blood-corpuscles,  and  hemic  masses  from  spleen  of 

dog 206 

166.  Section  through  human  spleen  showing  reticular  fibrils 206 

167.  Cover-glass  preparation  from  bone-marrov^'  of  dog 208 

168.  Section  through  human  red  bone-marrow      ...         209 

169.  Small  lobule  from  thymus  of  child,  well-developed  cortex 21 1 

170.  Hassall's  corpuscle  and  a  small  portion  of  medullary  substance  from  thymus 

of  child  ten  days  old  (Huber) 211 

171.  Cross-section  of  human  carotid  artery         217 

172.  Section  through  human  artery,  one  of  the  smaller  of  the  medium-sized  ...  217 

173.  Precapillary  vessels  from  mesentery  of  cat  (Huber) 218 

174.  Cross-section  of  human  internal  jugular  vein 219 

175.  Section  of  small  human  vein 220 

176.  Endothelial  cells  of  capillary  and  precapillary  from  mesentery  of  rabbit  (Huber)  221 

177.  Small  artery  from  oral  submucosa  of  cat  with  nerve-terminations 222 

178.  Section  of  a  cell-ball  from  glomus  caroticum  of  man 225 

179.  Thoma-Zeiss  hemocytometer 232 

180.  Section  through  lower  lip  of  man 237 

181.  Longitudinal  section  through  a  human  tooth,  showing  lines  of  Retzius    .    .    .  239 

182.  Portion  of  ground  tooth  from  man,  showing  enamel  and  dentin 240 

183.  Longitudinal  section  through  human  molar  from  the  center  of    the  enamel 

layer 241 

184.  Cross-section  of  human  tooth,  showing  cement  and  dentin 243 

185.  Nerve  termination  in  pulp  of  rabbit's  molar  (Huber) 244 

186-189.    Four  stages  in  the  development  of  tooth  in  sheep  embryo 245 

190.  Portion  of  cross-section  through  developing  tooth 246 

191.  Fungiform  papilla  from  human  tongue  (Huber) 247 

192.  Cross-section  of  human  tongue  showing  filiform  papillae     .    .             248 

193.  Longitudinal   section  of  foliate  papilla  of  rabbity  showing  taste-buds  (Huber)  249 

194.  Longitudinal  section  of  a  human  circumvallate  papilla 250 


14  ILLUSTRATIONS. 

FIG.  PAGE 

195.  Schematic  representation  of  a  taste-goblet  (Hermann) 251 

196,  197.   Section  through  pharyngeal  tonsil  of  man 252,  253 

198.  Section  through  salivary  gland  of  rabbit,  with  injected  blood-vessels    ....  255 

199.  Model  of  a  small  portion  of  a  sublingual  gland  of  man 256 

200.  Section  of  human  submaxillary  gland 257 

201.  Section  of  parotid  gland  of  man 257 

202.  Portion  of  a  model  of  a  salivary  gland  with  mucus  secretion 258 

203.  Alveoli  from  submaxillary  gland  of  dog  (Huber) 258 

204.  Model  of  a  gland  of  v.  Ebner,  from  a  boy        260 

205.  Section  of  esophagus  of  a  dog                 ....             263 

206.  Section  of  human  esophagus,  showing  a  cardiac  gland  with  a  dilated  duct  .    .  264 

207.  Epithelium  of  human  stomach,  covering  fold  of  mucosa  between  two  gastric 

crypts 266 

208.  Vertical  section  through  fundus  of  human  stomach  .    . 267 

209.  Fundus  glands  from  fundus  of  stomach  of  young  dog  ( Huber) 267 

210.  Section  through  junction  of  human  esophagus  and  cardia 268 

211.  Vertical  section  through  human  pylorus 270 

212.  Section  of  human  pylorus                         27 1 

213.  Section  through  fundus  of  human  stomach  in  condition  of  hunger 272 

214.  Section  through  fundus  of  human  stomach  during  digestion 272 

215.  Illustrations  of  models,  made  after  Bom's  wax-plate  reconstruction  method, 

of  glandular  structures  and  duodenal  villi  of  human  intestine 273 

216.  Section  through  mucous  membrane  of  human  small  intestine 275 

217.  Longitudinal  section  through  summit  of  villus  from  human  small  intestine  .    .  276 

218.  Section  through  the  junction  of  the  human  pylorus  and  duodenum 278 

219.  Section  of  solitary  lymph-nodule  from  vermiform  appendix  of  guinea-pig  .    .  279 

220.  Section  through  colon  of  man,  showing  glands  of  Lieberkühn      280 

221.  Transverse  section  of  human  vermiform  appendix  (Huber) 281 

222.  Solitary  lymph-follicle  from  human  colon 282 

223.  Section  through  fundus  of  injected  cat's  stomach 283 

224.  Schematic  transverse  section  of  human  small  intestine  (Mall) 285 

225.  Portion  of  the  plexus  of  Auerbach  from  stomach  of  cat  (Huber)      286 

226.  Section  of  esophagus  of  cat  showing  nerve-terminations  ( Huber) 287 

227.  Section  through  liver  of  pig,  showing  chains  of  liver-cells .    •  289 

228.  Section  through  injected  liver  of  rabbit 290 

229.  230.    Human  bile  capillaries                  291 

231.  Diagram  of  hepatic  cord  in  transverse  section 292 

232.  Section  through  the  human  liver,  showing  the  beginning  of  bile-ducts     .    .    .  292 

233.  Injected  blood-vessels  in  liver  lobule  of  rabbit 293 

235.  Reticulum  of  dog's  liver                  294 

236.  Connective  tissue  from  liver  of  sturgeon,  showing  reticulum           295 

237.  Liver  of  rabbit,  showing  the  so-called  stellate  cells  of  Kupfifer  (Huber)  ...  296 

238.  Section  through  liver  lobule  of  dog,  showing  stellate  cells 297 

239.  Transverse  section  through  alveolus  of  frog's  pancreas 299 

240.  Model  of  lobule  of  human  pancreas 299 

241.  242.    Section  through  human  pancreas •;■■.".    3°°>  3°^ 

243.  Relation  of  three  adjoining  alveoli  to  excretory  duct,   illustrating  origin   of 

centro-acinal  cells ■    • ^^^ 

244.  Section  of  human  pancreas,  showing  gland  alveoli   surrounding  an  area    of 

Langerhans  (Huber)       ...                      3°2 

245.  Vertical  section  through  mucous  membrane  of  human  larynx 309 

246.  Longitudinal  section  of  human  trachea  (Huber) 3^^ 

247.  Transverse  section  through  human  bronchus 3^2 

248.  249.    Sections  of  cat's  lungs    .....  ...  .■■.•••3^3 

250.  Internal  surface  of  human  respiratory  bronchiole  (Kölliker)      .......  314 

251.  Inner  surface  of  human  alveolus,  showing  respiratory  epithelium  (Kölliker)  .  315 

252.  Respiratory  epithelium  in  amphibia 3^^ 

253.  Scheme  of  lung  lobules  after  Miller .  ■      .   '    "  ^^^ 

254.  Reconstruction  in  wax  of  a  single  atrium  and  air-sac  with  the  alveoli  (Miller)  317 

255.  Section  of  human  lung,  showing  elastic  fibers  (Huber) 3^^ 

256.  Section  through  injected  rabbit's  lung 3^° 

257.  Cross-section  of  thyroid  gland  of  man  (Huber) 3^9 

258.  Section  from  parathyroid  of  man  (Huber) 321 

259.  Kidney  of  new-born  infant 323 

260.  Isolated  uriniferous  tubules 324 


ILLUSTRATIONS. 


15 


FIG.  PAGE 

261.  Median  longitudinal  section  of  adult  human  kidney 325 

262.  Section  of  cortical  substance  of  human  kidney                   326 

263.  Section  of  proximal  convoluted  tubules  from  man        ...                 327 

264.  Epithelium  from  proximal  convoluted  tubule  of  guinea-pig,  with  surface  and 

lateral  views ....  328 

265.  Cortical  portion  of  longitudinal  section  of  kidney  of  child  (Huber) 328 

266.  Section  of  medulla  of  human  kidney     ...                 329 

267     Longitudinal  section  through  papilla  of  injected  kidney 330 

268.  Section  through  junction  of  two  lobules  of  kidney 331 

269.  Diagrammatic  scheme  of  uriniferous  tubules  and  blood-vessels  of  kidney     .  ^33 

270.  Direct  anastomosis  between  an  artery  and  vein  in  a  column  of  Bertin  of  child  335 

271.  Section  of  lower  part  of  human  ureter               ,        ...  337 

272.  Transverse  section  of  the  wall  of  the  human  bladder,  giving  a  general  view 

of  its  structure 338 

273.  Section  of  suprarenal  cortex  of  dog       340 

274.  Arrangement  of  intrinsic  blood-vessels  in  cortex  and  medulla  of  dog's  adrenal 

(Flint) 341 

275.  Section  from  ovary  of  adult  dog  (Waldeyer) 345 

276.  Section  from  ovary  of  young  girl 34O 

277-280.    Sections  from  cat's  ovary 348 

281.  Transverse  section  through  the  cortex  of  a  human  ovary 349 

282.  Representation  of    behavior  of  the   chromatin  during  the   maturation   of  the 

ovum  (Riickert)        .    .                 •    •  3Si 

283.  Scheme  of  the  development  and  maturation  of  an  ascaris  ovum  (Boveri)     .    .  352 

284.  Section  of  oviduct  of  young  woman 355 

285.  Section  from  uterus  of  young  woman 357 

286.  Section  of  human  vagina  (Huber) 358 

287.  Section  of  human  labia  minora  (Huber)   .    .                      .         359 

288.  Diagram  showing  the  characteristics  of  spermatozoa  of  vertebrates 361 

289.  Human  spermatozoa     .    .                              362 

290.  Longitudinal  section  through  human  testis  and  epididymis 363 

291.  292.    Sustentacular  cells 364 

293.  Section  of  human  testis  (Huber) 365 

294.  Section  through  human  vasa  efferentia 366 

295.  Cross-section  of  vas  epididymidis  of  human  testis  (Huber) 366 

296.  Section  of  dog's  testis  with  injected  blood-vessels         367 

297.  Cross-section  of  vas  deferens  near  epididymis  (human)  (Huber) 368 

298.  Cross-section  of  wall  of  seminal  vesicle  (human)  (Huber) 369 

299.  Section  of  prostrate  gland  of  man  (  Huber)  .    .                 369 

300.  Schematic  diagram  of  spermatogenesis  as  it  occurs  in  ascaris  (Boveri)  ....  373 

301.  Schematic  diagram  of    section    through    convoluted    seminiferous    tubule    of 

mammal  (Hermann) 375 

302.  Section  of  convoluted  tubule  from  rat's  testicle 376 

303.  Under  surface  of  the  epidermis 380 

304.  Cross-section  of  skin  of  child  with  injected  blood-vessels 381 

305.  Prickle  cells  from  the  stratum  Malpighii  of  man 382 

306.  Cross-section  of  human  epidermis 383 

307.  Cross-section  of  negro's  skin 3S4 

308.  A  reconstruction,  showing  the  arrangement  of  the  blood-vessels  in  the  skin  of 

the  sole  of  the  foot  (Spaltcholz) 385 

309.  Nerves  of  epidermis  and  papillse  from  ball  of  cat's  foot '  .    .    .    .  386 

310.  311.    Meissner's  corpuscle  from  man 387 

312.  Grandry's  corpuscles  from  duck's  bill 388 

313.  Transverse  section  of  human  scalp                 • 390 

314.  Longitudinal  section  of  human  hair  and  follicle  .             391 

315.  Cross-section  of  human  hair  with  follicle       392 

316.  Longitudinal  section  of  cat's  hair  and  follicle,  showing  nerve-termination    .    .  393 

317.  Longitudinal  section  through  human  nail  and  its  groove 394 

318.  Transverse  section  through  human  nail  and  its  sulcus 395 

319.  Coiled  portion  of  a  sweat-gland  from  the  plantar  region  of  a  man,  reconstructed 

by  Born's  wax-plate  method  (Huber — Adamson) 396 

320.  Cross-section  of  coiled  tubule  of  sweat-glands  from  human  axilla      .    .         .    .  396 

321.  Tangential  section  through  coiled  tubule  of  sweat-glands  from  human  axilla  397 

322.  Sebaceous  gland  with  a  portion  of  the  hair  follicle,  reconstructed  by  Born's 

wax-plate  method 398 


lO  ILLUSTRATIONS. 

FIG.  PAGE 

323.  Section  of  alveoli  from  sebaceous  gland  of  human  scalp  (  Huber)     .         ...  399 

324.  Model  of  small  portion  of  a  secreting  mammary  gland        400 

325.  Section  of  mammary  gland  of  nullipara  (Nagelj .    ,  401 

326.  Transverse  section  through  human  skin 404 

327.  Cross-sections  of  human  spinal  cord 407 

328.  Schematic  diagram  of  spinal  cord  in  cross-section  (von  Lenhossek) 409 

329.  Schematic  cross-section  of  spinal  cord  (Ziehen)    .    .             410 

330.  Section  through  human  cerebellar  cortex  vertical  to  the  surface  of  the  convolution  413 

331.  Schematic  diagram  of  cei:ebellar  cortex 414 

332.  Cell  of  Purkinje  from  human  cerebellar  cortex 415 

233.   Granular  cell  from  the  granular  layer  of  the  human  cerebellar  cortex  ....  415 

334.  Vertical  section  of  human  cerebral  cortex 418 

335.  Large  pyramidal  cell  from  human  cerebral  cortex 419 

336.  Schematic  diagram  of  cerebral  cortex 420 

337.  Olfactory  bulb .......'....  422 

338.  Longitudinal  section  of  spinal  ganglion  of  cat  (Huber) 424 

339.  Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit  (Huber) 425 

340.  Diagram  showing  the  relations  of  the  neurones  of  a  spinal  ganglion  (Dogiel)  426 

341.  Neurone  from  inferior  cervical  sj'mpathetic  ganglion  of  a  rabbit  (Huber)     .    .  427 

342.  From  section  of  semilunar  ganglion  of  cat  (Huber) 428 

343.  From  section  of  stellate  ganglion  of  dog  (Huber) 429 

344.  From  section  of  sympathetic  ganglion  of  turtle  (Huber) .  430 

345.  From  section  of  sympathetic  ganglion  of  frog  (Huber) 430 

346.  Schematic  diagram  of  a  sensorimotor  reflex  arc  according  to  the  modern  neu- 

rone theory .     .  431 

347.  Schematic  diagram  of  a  sensorimotor  reflex  cycle ...  432 

348.  Schematic  diagram  of  the  reflex  tracts  between  a  peripheral   organ  and  the 

brain  cortex           .    .         ...         ■ 433 

349.  Neurogliar  cells  (Huber) ...  434 

350.  Neurogliar  cells  from  cross-section  of  the  white  matter  of  the  human  spinal 

cord  (Huber)     ...             436 

351.  Section  through  injected  cerebral  cortex  of  rabbit 438 

352.  Schematic  diagram  of  the  eye  (Leber  and  Flemming) 447 

353-    Section  through  the  anterior  portion  of  human  cornea 449 

354.    Corneal  spaces  of  dog 450 

355-    Section  through  the  human  choroid 452 

356.  Meridional  section  of  the  human  ciliary  body 454 

357.  Injected  blood-vessels  of  the  human  choroid  and  iris  . •.    .    .  456 

358.  Section  of  the  human  retina 458 

359-    Section  through  point  of  entrance  of  human  optic  nerve 460 

360.  Section  through  human  macula  lutea  and  fovea  centralis 461 

361.  Schematic  diagram  of  the  retina  (Ramon  y  Cajal) 463 

362.  Injected  blood  vessels  of  the  human  retina 465 

363.  Injected  blood-vessels  of  human  macula  lutea  .    .    .    .■ 466 

364.  Vertical  section  of  upper  eyelid  of  man 471 

365.  Meibomian  or  tarsal  gland,  reconstructed  after  Born' s  wax -plate  method  .    .    .  472 

366.  Schematic  representation  of  the  complete  auditory  apparatus  (Schwalbe)     .    .  477 

367.  Cross-section  of  the  Eustachian  tube  ...                 479 

368.  Right  bony  labyrinth  (Quain,  after  Sömmering) 480 

369.  Membranous    labyrinth    from    five-month    human    embryo    (Schwalbe,    after 

Retziiis) 481 

370.  Transverse  section  through  an  osseous  and  membranous  semicircular  canal  of 

an  adult  human  being 482 

371.  Vertical  section  through  the  anterior  ampulla    .    .    •    ■ 484 

372.  Longitudinal  section  of  the  cochlea  of  a  cat 486 

373.  Section   through  a  turn  of  the  osseous  and  membranous  cochlear  duct  of  the 

cochlea  of  guinea-pig      487 

374.  Organ  of  Corti  (Retzius) 490 

375-    Surface  of  organ  of  Corti,  with  surrounding  structures  (Retzius) 493 

376.  Scheme  of  distribution  of  blood-vessels  in  labyrinth  ( Eichler)      495 

377.  Portion  of  transverse  section  of  the  olfactory  region  of  man 499 


INTRODUCTION   TO   MICROSCOPIC 
TECHNIC. 

I.    THE  MICROSCOPE  AND  ITS  ACCESSORIES, 

A  detailed  description  of  the  microscope  and  its  accessory  appa- 
ratus hardly  lies  within  the  scope  of  this  book.  If,  notwithstanding, 
a  few  points  be  touched  upon,  it  is  done  only  that  the  beginner 
may  have  a  working  knowledge  of  the  different  parts  of  the  instru- 
ment which  he  must  use.  A  more  intimate  knowledge  of  the  theory 
of  the  microscope  may  be  acquired  by  studying  such  works  as 
those  of  Dippel,  A.  Zimmermann,  and  Carpenter. 

Histologic  specimens  are  examined  with  the  aid  of  the  micro- 
scope, an  instrument  which  magnifies  the  objects  by  means  of  its 
optic  apparatus.  For  this  purpose  simple  microscopes,  consisting 
of  one  or  more  converging  lenses  or  lens  systems  may  be  used, 
though  they  generally  do  not  give  sufficient  magnification  to  be  of 
much  service  in  the  study  of  histologic  specimens  ;  they  give  an 
erect  image  of  the  object  observed.  When  greater  magnification 
is  desired,  it  is  necessary  to  use  a  compound  microscope,  consist- 
ing generally  of  two  or  more  lens  systems,  giving  an  enlarged, 
inverted,  real  image  of  the  object  observed.  The  lens  system  of  a 
compound  microscope  may  be  changed  according  to  the  needs  of 
the  case,  and  thus  a  variation  in  the  magnification  of  the  object 
obtained.  The  rest  of  the  instrument  consists  of  a  framework 
called  the  stand,  the  lower  portion  of  which  consists  of  a  foot- 
plate or  base.  From  the  base  rises  the  column  or  pillar,  to 
which  the  other  parts  of  the  microscope  are  attached.  From  below 
upward  come  the  movable  mirror,  the  stage  and  substage  with 
diaphragm  and  condenser,  and  the  tube  with  pinion  and  fine  adjust- 
ment. One  side  of  the  mirror  is  concave,  and  serves  to  concentrate 
the  rays  of  light  in  the  direction  of  a  central  opening  in  the  stage. 
The  other  side  is  plane.  If  the  objects  are  to  be  examined  by 
direct  illumination,  and  not  by  transmitted  light,  the  mirror  is  so 
placed  that  the  rays  are  reflected  away  from  the  opening  in  the  stage. 
The  specimen  to  be  examined  is  placed  on  the  stage,  over 
the  central  opening.  If  the  light  be  too  strong,  the  opening  may 
be  diminished  in  size  by  means  of  a  diaphragm.  In  some  instru- 
ments these  diaphragms  are  placed  in  the  opening  of  the  stage,  and 
consist  of  plates  with  different  sized  apertures.  A  better  form  is 
composed  of  one  large  disc  containing  several  apertures  of  different 
sizes.  This  is  fastened  to  the  under  surface  of  the  stage  in  such  a 
way  that  by  revolving  the  disc  the  apertures  may  be  brought  one 

2  17 


i8 


THE    MICROSCOPE    AND    ITS    ACCESSORIES. 


after  the  other  opposite  the  opening  in  the  stage.  A  much  better 
diaphragm,  constructed  on  an  entirely  different  principle,  is  the  so- 
called  iris  diaphragm.  Although  its  opening  is  not  exactly  circu- 
lar, yet  it  has  the  advantage  of  being  easily  enlarged  or  contracted 
by  manipulating  a  small  handle  controlling  the  metal  plates  sliding 
over  one  another. 

The  tube,  which  is  contained  in  a  close-fitting  metal  sheath, 
is  attached  to  the  upright  of  the  microscope.      In  the  simpler  forms 


Rack  and  pinion  for 
coarse  adjustment. 


Micrometer  screw  for 
fine  adjustment. 


Iris  diaphragm  and 
Abbe  condenser. 


Screw  for  focusing 
condenser. 


Pillar. 


Stand. 


Fig.  I. — Microscope. 


of  microscopes  the  tube  is  raised,  lowered,  or  twisted  by  hand.  In 
more  complicated  instruments  the  upward  and  downward  move- 
ments are  accomplished  by  means  of  a  rack  and  pinion — coarse 
adjustment.  A  micrometer  screw — fine  adjustment — situated 
at  either  the  upper  or  the  lower  end  of  the  upright,  controls  the  fine 
adjustment.  The  tube  possesses  an  upper  and  a  lower  opening,  into 
which  lenses  may  be  laid  and  screwed.  The  ocular,  into  the  ends 
of  which   lenses   are   inserted,   fits   into  the   upper  opening.      The 


LENSES.  19 

upper  is  called  the  ocular  lens,  the  lower  the  collective  lens.  The 
objective  system,  which  is  a  combination  of  several  lenses  or  lens 
systems,  the  lowest  and  smallest  of  which  is  known  as  the  fj'ont 
lens,  is  screwed  into  the  lower  opening  of  the  tube. 

All  larger  instruments  possess  several  oculars  and  objec- 
tives, which  together  give  different  magnifications  according  to  the 
combinations  used.  For  most  objects  a  magnification  of  500  diam- 
eters is  all  that  is  required,  but  to  obtain  this  and  still  have  a 
clear  and  bright  field  the  ordinary  lenses  are  hardly  sufficient.  The 
greater  the  magnification,  the  darker  is  the  field.  To  avoid  this, 
illuminating  mechanisms  (condensers,  Abbe's  apparatus)  have  been 
constructed,  by  means  of  which  the  rays  of  light  are  concentrated 
and  controlled.  This  arrangement  is  absolutely  necessary  for  deli- 
cate work. 

Even  with  the  aid  of  such  an  apparatus  the  dry  objective  sys- 
tems are  not  sufficient.  With  them  the  rays  of  light  must  pass 
through  different  media  having  various  indices  of  refraction.  The 
rays  pass  from  the  object  through  the  cover-slip,  and  then  through 
the  air  between  the  latter  and  the  objective  system.  They  are  thus 
deflected  in  different  directions — a  defect  which  would  be  avoided 
if  the  rays  were  made  to  pass  through  a  single  medium.  This  latter 
condition  may  be  practically  brought  about  by  placing  between  the 
objective  and  the  cover-glass  a  drop  of  some  fluid  having  about  the 
same  refractive  index  as  the  glass.  The  lens  is  then  lowered  into 
the  fluid.  As  this  invention  has  proved  useful,  so-called  immersion 
lenses  have  been  made  during  recent  years.  There  are  thus  twa 
kinds  of  lens  systems — the  dry  and  the  immersion  lenses.  The 
latter  are  divided  into  two  groups — lenses  with  water  and  those 
with  oil  immersion.  As  oil  has  a  greater  index  of  refraction  than 
water,  and  one  more  nearly  approaching  that  of  glass,  the  oil- 
immersion  lenses  are  at  present  the  best  objectives  that  we  possess. 
Karl  Zeiss,  of  Jena,  and  other  microscope  makers,  have  in  late 
years  made  lenses  from  a  special  sort  of  glass  which  reduces  to  a 
minimum  the  chromatic  and  spheric  aberration  of  the  rays  of  light 
in  their  passage  through  the  objective  (apwchromatic  lenses). 

The  rays  of  light  reflected  from  the  mirror  and  passing 
through  the  object  are  refracted  by  the  objective  system  in  such  a 
way  that  they  are  focused  in  a  so-called  real  image  at  a  point  about 
half-way  up  the  tube.  This  picture  is  an  inverted  one,  the  right 
side  of  the  microscopic  field  being  at  the  left  of  the  real  image,  and 
the  upper  portion  below.  The  picture  is,  in  other  words,  rotated 
1 80  degrees.  By  means  of  the  ocular  the  real  image  is  again  mag- 
nified— virtual  image — but  no  longer  inverted,  although  to  the  eye 
of  the  microscopist  the  field  actually  appears  inverted.  To  shut  out 
the  rays  of  light,  which  cause  a  diffused  picture,  diaphragms  are 
sometimes  introduced  into  the  tube  as  well  as  into  the  ocular.  (See 
Fig.  2.) 

The  objects  to  be  examined  are  placed  upon  a  glass  plate 


20 


THE    MICROSCOPE    AND    ITS    ACCESSORIES. 


called  a  slide.  Microscopic  slides  are  of  different  sizes,  and  are 
usually  oblong  in  shape.  Those  in  most  common  use  are  three 
inches  long  and  an  inch  wide.  The  object  is  covered  by  a  very 
much  smaller  and  thinner  glass  plate — the  cover=slip.     The  whole 

preparation  is  then  placed  upon  the 
stage  in  such  a  way  that  the  cover- 
slip  is  upward  and  immediately  be- 
neath the  end  of  the  tube.  The 
mirror  of  the  microscope  is  now  so 
adjusted  as  to  concentrate  the  rays  of 
light  on  the  preparation,  illuminating 
it  as  much  as  is  necessary.  By  means 
of  the  rack  and  pinion,  or  coarse 
adjustment,  the  whole  tube  is  now 
slowly  lowered  toward  the  cover-slip 
until  the  bare  outlines  of  the  object 
are  dimly  seen  in  the  white  field. 
From  this  point  on,  the  micrometer 
screw,  or  fine  adjustment,  is  used  in 
bringing  the  front  lens  down  to  its 
proper  focal  distance  from,  the  prep- 
aration. The  object  is  now  seen  to 
be  clear  and  well  defined.  By  turn- 
ing the  screw  to  the  right  or  the  left, 
different  parts  of  the  specimen  are 
brought  more  clearly  into  view,  this 
result  being  due  to  the  fact  that  not 
all  points  in  the  preparation  are  in  the 
same  plane. 

In  studying  objects  it  is  always 
well  to  draw  them,  using  a  sharpened 
pencil  and  smooth  paper.  The  be- 
ginner soon  finds  that  with  constant 
practice  he  can  sketch  the  different 
parts  of  the  field  in  nearly  their  proper 
relationship.  This  by  no  means  easy 
work  is  facilitated  by  the  use  of  a 
drawing  apparatus  called  the  camera 
lucida.  The  best  of  these  is  that 
devised  by  Abbe.  It  is  fastened  to 
the  upper  end  of  the  tube,  above  the 
ocular.  The  apparatus  is  so  made 
that  both  the  preparation  and  the 
drawing  surface  are  seen  by  the  same 
eye.  The  microscopic  field  is  seen  directly,  while  the  drawing  sur- 
face is  made  visible  by  means  of  a  mirror.  When  the  apparatus 
is  in  place  and  the  drawing  commenced,  it  appears  to  the  one 
sketching  as  if  his  pencil  were  moving  over  the  preparation  itself 


Fig.  2. — Diagram  showing  the 
principle  of  a  compound  microscope 
with  the  course  of  the  rays  from  the 
object  [a  b)  through  the  objective 
to  the  real  image  {b^  a^),  thence 
through  the  ocular  and  into  the  eye 
to  the  retinal  image  [a"^  P),  and 
the  projection  of  the  retinal  image 
into  the  field  of  vision  as  the  virtual 
image  {b^  «'). — (Fig  21,  Gage,  The 
Microscope,  eighth  edition. ) 


SECTIONS    OF    FRESH    TISSUES.  21 

Outlines  are  reproduced  on  paper  with  great  exactness  both  as 
to  form  and  size  ;  finer  details  must  of  course  be  sketched  in  free 
hand. 

Every  preparation  should  first  be  examined  with  a  low  power, 
and  only  after  the  student  has  studied  the  specimen  as  a  whole  and 
found  instructive  areas  should  the  higher  powers  be  used. 


n,  THE  MICROSCOPIC  PREPARATION. 

In  many  cases  the  making  of  a  microscopic  preparation  is  a  very 
simple  procedure,  especially  when  fresh  objects  are  to  be  examined.  A 
drop  of  blood,  for  instance,  may  simply  be  placed  upon  a  slide,  covered 
with  a  cover-slip,  and  examined.  Other  objects,  as  the  mesentery,  thin 
transparent  nerves,  detached  epithelia,  spermatozoa,  etc.,  need  no  further 
preparation,  but  may  be  examined  at  once. 

Portions  of  larger  organs  are  often  studied  after  having  been 
teased,  which  may  be  done  by  means  of  two  needles  fastened  in  handles. 
If  the  objects  be  composed  of  fibers  running  in  parallel  directions,  one 
needle  is  thrust  into  the  substance  to  hold  it  in  place,  while  the  other  is 
used  to  tear  the  fibers  apart.  This  method  is  used  in  examining  muscles, 
nerves,  tendons,  etc. 

Some  tissues  are  so  constituted  that  they  can  only  be  investigated  by 
means  of  sections,  which  permit  a  study  of  their  elements  and  the  rela- 
tionship  of  the  same  to  each  other.  In  this  method  an  ordinary  razor, 
moistened  in  some  fluid,  may  be  employed.  As  a  rule,  it  is  not  the  size 
of  the  section,  but  the  thinness,  which  is  important.  This  latter  is 
obtained  only  by  practice.  Every  microscopist  ought  to  become  accus- 
tomed to  making  free-hand  sections  with  the  razor.  It  is  the  simplest  of 
all  methods,  is  very  rapid,  and  is  especially  useful  in  the  quick  identifica- 
tion of  a  tissue.  In  cutting  fresh  so-called  parenchymatous  tissues,  such 
as  liver  and  kidney,  an  ordinary  razor  is  not  sufficient.  Here  a  double 
knife  is  necessary.  This  consists  of  two  blades,  which  are  so  placed  one 
above  the  other  that  their  distal  ends  touch,  while  their  proximal  ends 
are  slightly  separated.  The  distance  of  the  blades  from  each  other  is 
regulated  by  a  screw.  If  this  be  removed  the  knives  may  be  separated 
for  cleaning.  In  making  sections,  only  those  portions  of  the  blades 
are  of  importance  which  are  very  close  together  but  do  not  actually 
touch.  Sections  are  cut  by  drawing  the  moistened  instrument  quickly 
through  an  organ,  as,  for  instance,  a  fresh  liver.  As  the  organ  is  cut  in 
two,  a  very  thin  section  of  the  tissue  remains  between  the  blades.  This 
is  removed  by  taking  out  the  screw  and  separating  the  blades  in  normal 
salt  solution.  Organs  of  a  similar  consistence  can  be  frozen  and  then  cut 
with  an  ordinary  razor  the  blade  of  which  has  been  cooled.  Sometimes 
good  results  may  be  obtained  by  drying  small  pieces  of  tissue,  as,  tor 
instance,  tendon. 

As  sections  or  small  pieces  of  fresh  tissue  would  soon  become 
dry  when  placed  on  the  slide,  they  must  be  kept  moist  during  examina- 
tion. They  are  therefore  mounted  in  so-called  indifferent  fluids 
(placed  on  the  slide  and  immersed  in  a  few  drops  of  the  indifferent  fluid 
and  covered  with  a  cover-slip").  These  have  the  power  of  preserving 
living  tissues  for  some  time  without  change.     Such  fluids,  for  instance,  are 


22  THE    MICROSCOPIC    PREPARATION. 

the  lymph,  the  aqueous  humor,  serous  fluids,  amniotic  fluid,  etc.  Artifi. 
cial  indifferent  fluids  are  much  used  and  should  always  be  kept  in  stock. 
Of  this  class,  the  following  are  useful : 

1.  Physiologic  saline  solution:  A  0.75^  solution  of  sodium 
chlorid  in  distilled  water. 

2.  Schultze's  iodized  serum:  A  saturated  solution  of  iodin  or 
tincture  of  iodin  in  amniotic  fluid. 

3.  Ranvier's  solution  of  iodin  and  potassium  iodid  :  A  satu- 
rated solution  of  iodin  in  a  2^  solution  of  potassium  iodid. 

4.  Kronecker' s  fluid  :  Distilled  water,  100  c.c. ;  sodium  chlorid, 
5  gm.;  sodium  carbonate,  0.06  gm. 

5.  Solution  of  Ripart  and  Petit :  Copper  chlorid,  0.3  gm.  ;  cop- 
per acetate,  0.3  gm.  ;  aqua  camphorse,  75  c.c.  ;  distilled  water, 
75  c.c.  ;  and  glacial  acetic  acid,  i  c.c.  After  mixing,  this  solution 
is  yellow,  but  clears  up  within  a  few  hours,  and  should  then  be 
filtered. 

The  examination  of  fresh  tissues  comes  far  from  revealing  all  the 
finer  details  of  their  structure.  This  is  partly  due  to  the  fact  that  the 
indices  of  refraction  of  the  different  elements  of  the  tissues  are  too  nearly 
alike,  in  consequence  of  which  the  outlines  are  somewhat  dimmed  ;  and 
also,  that  changes  occur,  even  during  the  most  careful  manipulation  of 
the  tissues,  which  result  in  pictures  somewhat  different  from  the  normal. 
With  many  tissues  and  organs  while  yet  fresh  it  is  also  somewhat  difficult 
to  obtain  a  separation  of  their  constituent  elements.  It  is  therefore 
generally  necessary  to  subject  tissues  or  organs  to  special  methods  of 
treatment  before  they  may  be  studied  microscopically  with  any  degree 
of  profit.  Certain  of  these  methods,  such  as  have  proved  by  experience 
to  possess  reliability,  shall  receive  consideration  in  the  following  pages. 

METHODS  OF  MACERATION. 

The  reagents  employed  for  the  maceration  of  tissues  have  in  general 
the  property  of  softening  or  removing,  partly  or  completely,  certain  con- 
stituents of  the  tissues,  while  they  at  the  same  time  harden  or  fix  other 
tissue  elements.  Generally  the  ground-substance  or  intercellular  sub- 
stance is  softened  or  removed  while  the  cellular  or  other  constituents 
undergo  fixation.  Tissues  thus  treated  when  subjected  to  teasing, 
crushing,  shaking,  or  brushing  with  a  camel' s-hair  brush,  are  readily 
broken  up  into  their  constituent  elements,  giving  useful  and  instructive 
preparations. 

1.  Alcohol,  30^  (Ranvier).  Dilute  one  volume  of  alcohol 
(95%)  with  two  volumes  of  distilled  water.  Small  pieces  of 
tissue  are  macerated  in  this  solution  in  twenty-four  hours  to  forty- 
eight  hours.  It  is  often  advantageous  to  fix  the  pieces  thus 
macerated  for  about  an  hour  in  i^  to  i^  osmic  acid.  Useful 
for  macerating  epithelia. 

2.  Dilute  solutions  of  chromic  acid,  i^  to  yü"%-  Small 
pieces  of  tissue  remain  in  this  solution  one  to  several  days.  Use- 
ful for  macerating  epithelia. 

3.  Concentrated  aqueous  solution  of  caustic  potash.  Small 
pieces  of  tissue  are  macerated  in  fifteen  minutes  to  an  hour. 
They  are  then  transferred  to  a  saturated  aqueous  solution  of  acetate 


FIXING    METHODS.  23 

of  potassium,  which  interrupts  the  action  of  the  macerating  fluid. 
Useful  for  macerating  epithelia  and  involuntary  and  heart  muscle. 

4.  Hydrochloric  acid,  20^  to  30%  aqueous  solution.  Mace- 
rates small  pieces  of  tissue  in  twelve  to  twenty-four  hours.  The 
pieces  are  then  thoroughly  washed  in  water.  Useful  for  isolating 
the  uriniferous  tubules  and  macerating  glands. 

5.  Nitric  acid,  10^  to  20^  aqueous  solution  or  made  up  with 
normal  salt  solution.  Macerates  small  pieces  of  tissue  in  twenty- 
four  to  forty-eight  hours.  Wash  thoroughly  in  water.  Useful  for 
macerating  involuntary  and  voluntary  muscle. 

6.  J.  B.  MacCallum  ("Contributions  to  Medical  Science," 
Baltimore,  1900)  recommends  the  following  nitric  acid  mixture 
for  isolating  heart -muscle  fibers  of  embryos  and  adults  :  Nitric 
acid,  I  part ;  glycerin,  2  parts ;  water,  2  parts.  The  hearts 
remain  in  this  fluid  from  eight  hours  to  three  days,  according  to 
their  size,  and  are  then  transferred  to  a  5  ^  aqueous  solution  of 
glycerin.  This  method  is  especially  useful  for  obtaining  prepara- 
tions showing  the  arrangement  of  the  heart -muscle  fibers. 

7.  Nitric  acid  and  chlorate  of  potassium  (Schulze).  Powder 
the  chlorate  of  potassium  and  add  sufficient  nitric  acid  to  make  a 
thin  paste.  Embed  the  tissue  to  be  macerated  in  this  paste,  in 
which  they  remain  from  one  to  several  hours.  They  are  then 
washed  in  water.  Useful  for  isolating  the  branched,  voluntary 
muscle -fibers  of  the  tongue  of  a  frog. 

8.  Concentrated  sulphuric  acid.  Useful  for  isolating  the  corni- 
fied  cells  of  the  epidermis,  nails,  and  hair. 

FIXING  METHODS. 

The  fixing  fluids  most  used  for  general  purposes  are  the  following : 
Alcohol. — Alcohol  is  frequently  used  as  a  fixing  fluid.  It  is  at 
the  same  time  a  hardening  fluid,  as  the  water  of  the  tissues  is  withdrawn 
and  their  albumin  coagulated.  Small  or  thin  pieces  are  put  immediately 
into  absolute  alcohol,  in  which  they  remain  for  from  twelve  to  twenty- 
four  hours.  The  period  required  for  fixation  may  be  greatly  shortened 
by  changing  the  absolute  alcohol  at  the  end  of  one  or  two  hours.  In 
the  case  of  larger  pieces,  a  successive  immersion  in  gradually  increasing 
strengths  of  alcohol  (50%,  70%,  90%)  is  the  method  chosen.  Pieces 
I  CO.  in  size  remain  for  twenty-four  hours  in  each  grade  of  alcohol, 
larger  pieces  for  a  proportionately  longer  time.  Alcohol  used  in  this  way 
is  a  hardening  fluid  rather  than  a  fixing  fluid. 
Carnoy's  Acetic=aIcohol  Mixture. — 

Glacial  acetic  acid I  part. 

Absolute  alcohol 3  parts. 

Fixes  very  rapidly.  Pieces  of  i  centimeter  in  thickness  are  fixed  in 
one -half  hour  to  one  hour.  The  after-treatment  is  with  absolute  alcohol, 
which  should  be  renewed  at  the  end  of  twenty-four  hours. 

Carnoy's  Acetic  Acid=alcohol=chloroform  Mixture. — 

Glacial  acetic  acid I  part. 

Chloroform 3  parts. 

Absolute  alcohol 6     " 

Fixes  very  rapidly,  even  larger  pieces  in  from  one-half  to  one  hour. 
The  after-treatment  is  with  absolute  alcohol. 


24  THE    MICROSCOPIC    PREPARATION. 

Osmic  acid  is  a  reagent  that  kills  quickly,  fixes  protoplasm  exceed- 
ingly well,  but  nuclei  not  so  well,  and  colors  certain  tissues.  Only 
small  pieces  can  be  fixed  in  this  fluid,  as  it  does  not  easily  penetrate  the 
tissues.  It  is  ordinarily  used  in  a  ^^  to  i^  aqueous  solution,  the 
objects  remaining  immersed  twenty-four  hours.  They  are  then  washed 
in  running  water  for  the  same  length  of  time,  after  which  they  are  trans- 
ferred to  90^  alcohol.  Very  small  objects  may  be  treated  with  osmic 
acid  in  the  form  of  vapor  (vaporization).  This  is  done  as  follows:  A 
very  small  quantity  of  osmic  acid  solution  is  put  in  a  small  dish.  The 
object  is  then  suspended  by  a  thread  in  such  a  way  that  it  does  not  come 
in  contact  with  the  fluid.  The  dish  should  be  covered  with  a  well -fitting 
lid. 

Flemming's  Solution. — A  solution  with  a  similar  action,  but  fixing 
nuclear  structures  better  than  osmic  acid,  is  the  chromic-osmic-acetic 
acid  solution  of  Flemming  : 

Osmic  acid,  I  %  aqueous  solution  .    .    .    ,  lo  parts. 
Chromic  acid,  I  %  aqueous  solution    ...  25      " 
Glacial  acetic  acid,  1%  aqueous  solution  .  10     " 
Distilled  water 55     " 

Small  pieces  are  fixed  in  a  small  quantity  of  the  fluid  for  at  least 
twenty- four  hours,  sometimes  for  a  longer  period,  extending  even  to 
weeks.  They  are  then  washed  for  twenty-four  hours  in  running  water  and 
passed  through  50%,  70%,  and  80%,  each  twenty-four  hours,  into  90% 
alcohol. 

Flemming  also  recommends  a  stronger  solution,  which  is  made  as 
follows  : 

Osmic  acid,  2^  aqueous  solution     ....    4  parts. 
Chromic  acid,  i  %  aqueous  solution     ...  1 5      " 
Glacial  acetic  acid I  part. 

Fol's  Solution. — Fol  has  recommended  the  following  modification 
of  Flemming's  solution  : 

Osmic  acid,  i  ^  aqueous  solution     ....     2  parts. 
Chromic  acid,  l^  aqueous  solution     ...  25      " 
Glacial  acetic  acid,  2^  aqupous  solution    .     5      *' 
Distilled  water 68     " 

The  after-treatment  is  the  same  as  for  Flemming's  solution. 

Hermann's  Solution. — Very  good  results  sometimes  follow  the 
use  of  the  platinum -acetic-osmic  acid  solution  of  Hermann  (89,  i).  It 
is  employed  as  is  Flemming's  solution  : 

Osmic  acid,  2  ^  aqueous  solution    ....    4  parts. 
Platinum  chlorid,  i^  aqueous  solution  .    .  15     " 
Glacial  acetic  acid I  part. 

After  fixing  with  this  solution,  Flemming's  solution,  or  any  other 
osmic  mixture,  the  subsequent  treatment  with  alcohol  may  be  followed 
by  crude  pyroligneous  acid.  The  objects  are  placed  for  from  twelve  to 
twenty-four  hours  in  the  latter  and  then  again  immersed  in  alcohol.  The 
result  is  a  peculiar  coloring  of  the  specimen  which  often  makes  subsequent 
staining  (see  below)  unnecessary  (Hermann). 

Corrosive  Sublimate. — An  excellent  fixing  fluid  is  made  by 
saturating  distilled  water  or  a  physiologic  saline  solution  (see  p.  22)  with 


FIXING    METHODS.  2$ 

corrosive  sublimate.  Small  pieces,  about  0.5  cm.  in  diameter,  are  im- 
mersed in  this  fluid  for  from  three  to  twenty-four  hours,  are  then  washed 
in  running  water  for  twenty-four  hours,  and  then  transferred  into  70^ 
alcohol.  After  twenty-four  hours  the  tissues  are  placed  in  80'/^  for  the 
same  length  of  time,  and  then  preserved  in  90^  alcohol.  It  often 
occurs  that  after  changes  in  temperature  crystals  of  sublimate  are  formed 
on  the  surface  or  in  the  interior  of  the  object.  For  their  removal  a  few 
drops  of  a  solution  of  iodin  and  potassium  iodid  are  added  to  the  alcohol 
(P.  Mayer).  It  is  a  matter  of  indifference  whether  the  joc/r,  80^  or 
90  f^  alcohol  is  thus  iodized.  In  the  further  treatment  of  the  object,  as 
well  as  in  sectioning,  any  such  crystals  of  sublimate  will  not  be  found  to 
be  a  hindrance.  Indeed,  in  the  case  of  very  delicate  objects  it  is  often 
more  advantageous  to  undertake  their  removal  qfta-  sectioning  by  adding 
iodin  to  the  absolute  alcohol  then  used. 

Acetic  Sublimate  Solution. — This  is  an  excellent  fluid,  and  at 
present  much  used  for  embryonic  tissues  and  for  organs  containing  only  a 
small  quantity  of  connective  tissue.  To  a  saturated  aqueous  solution  of 
sublimate,  5^  to  lo^/c  of  glacial  acetic  acid  is  added.  After  remaining 
two  or  three  hours  or  more  in  this  solution,  the  objects  are  transferred  to 
35^  alcohol,  after  which  they  are  passed  through  the  higher  grades  of 
alcohol. 

Picric  Acid. — Small  and  medium -sized  objects  (up  to  i  c.c.) 
are  fixed  in  twenty-four  hours  in  a  saturated  aqueous  solution  of  picric 
acid  (about  0.75^),  although  an  immersion  lasting  for  weeks  is  not 
detrimental,  especially  if  the  objects  be  of  considerable  size.  The  tissues 
are  transferred  to  70 'y^  or  80^  alcohol,  in  which  they  remain  until  the 
alcohol  is  not  colored  by  the  picric  acid.  They  are  then  preserved  in 
go(/c  alcohol. 

Instead  of  a  pure  solution  of  picric  acid,  the  picrosulphuric  acid 
of  Kleinenberg  or  the  picric=nitric  acid  of  P.  Mayer  may  be  used. 
The  first  is  made  thus:  i  c.c.  of  concentrated  sulphuric  acid  is  added 
to  100  c.c.  of  a  saturated  aqueous  picric  acid  solution.  This  is  allowed 
to  stand  for  tvventy-four  hours,  then  filtered,  and  diluted  with  double  its 
volume  of  distilled  water.  The  picric-nitric  acid  solution  is  made  by 
adding  2  c.c.  of  pure  nitric  acid  to  100  c.c.  of  a  saturated  picric  acid 
solution.      Filter  after  standing  for  twenty-four  hours. 

Rabl's  Solutions. — C.  Rabl  (94)  recommends  the  following 
mixtures,  especially  for  embryos  :  (i)  Concentrated  aqueous  solution  of 
corrosive  sublimate,  i  vol.  ;  concentrated  aqueous  solution  of  picric 
acid,  I  vol.  ;  distilled  water,  2  vols.  (2)  i  per  cent,  aqueous  solution 
of  platinum  chlorid,  i  vol.  ;  concentrated  aqueous  solution  of  corrosive 
sublimate,  i  vol.  ;  distilled  water,  2  vols.  In  both  cases,  after  being 
washed  twelve  hours  in  water  (in  the  first  preferably  in  alcohol)  the 
specimens  are  transferred  to  gradually  increased  strengths  of  alcohol. 

Vom  Rath's  Solutions. — O.  vom  Rath  (95)  recommends,  among 
others,  the  following  two  solutions:  (i)  Picric=osmic=acetic  acid 
solution.  Add  to  1000  c.c.  of  a  cold  saturated  picric  acid  solution  i 
gm.  of  osmic  acid,  and  after  several  hours  4  c.c.  of  glacial  acetic  acid. 
Objects  are  fixed,  according  to  their  size,  in  four,  fourteen,  and  forty- 
eight  hours,  and  then  transferred  to  75%  alcohol.  (2)  Picric=sub= 
limate=osmic  acid  solution.  A  mixture  of  100  c.c.  of  a  cold 
saturated  aqueous  picric  acid  solution  with  100  c.c.  of  saturated  sublimate 
solution  is  made,  into  which  is  poured  20  c.c.  of  a  2  f^  osmic  acid  solu- 


26  THE    MICROSCOPIC    PREPARATION, 

tion.  2  c.c.  of  glacial  acetic  acid  may  also  be  added.  Tissues  fixed  by 
either  of  these  fluids  may  be  treated  with  pyroligneous  acid  or  tannin. 
The  crystals  of  sublimate  must  be  removed  by  iodized  alcohol. 

Nitric  Acid. — Small  objects  may  be  fixed  in  about  six  hours  in 
3%  to  5^  nitric  acid  (sp.  gr.  1.4).  A  longer  immersion  is  injurious, 
as  certain  nuclear  structures  are  affected.  After  washing  thoroughly  in 
running  water,  the  tissues  are  treated  as  usual  with  alcohols  of  increasing 
concentration. 

Chromic  acid  is  used  in  a  yz%  to  1%  aqueous  solution. 
Small  pieces  are  fixed  for  twenty-four  hours,  larger  ones  for  a  longer  time, 
even  weeks.  The  quantity  of  the  fixing  fluid  should  be  at  least  more 
than  fifty  times  the  volume  of  the  tissues  to  be  fixed.  The  objects  are 
subsequently  washed  in  running  water  and  run  through  the  ascending 
alcohols.     This  last  should  be  done  in  the  dark. 

Two  or  3  drops  of  formic  acid  may  be  advantageously  added  to 
each  100  c.c.  of  chromic  acid  solution  (C.  Rabl). 

Müller's  Fluid.— 

Potassium  bichromate 2  to  2.5  gm. 

Sodium  sulphate i        " 

Water loo     c.c. 

With  this  solution  it  requires  several  weeks  for  proper  fixation,  and  the 
process  must  be  conducted  in  the  dark.  During  the  first  few  weeks  the 
solution  should  be  changed  every  few  days,  and  later  once  a  week. 
According  to  the  results  desired,  the  pieces  are  either  washed  out  in  run- 
ning water  and  subsequently  treated  in  the  usual  manner  with  alcohol,  or 
they  are  placed  directly  in  70^,  which  is  later  replaced  by  80  (fo  and 
90^  alcohol.  It  is  important  that  all  these  procedures  should  take  place 
in  the  dark. 

The  use  of  Erlicki's  fluid  (potassium  bichromate,  2^  gm.;  cupric 
sulphate,  0.5  gm.,  and  water,  100  c.c.)  is  quite  similar  to  that  of 
Müller's,  except  that  it  acts  much  more  quickly.  A  temperature  of  30° 
C.  to  40°  C.  shortens  the  process  in  both  cases  considerably,  Müller's 
fluid  fixing  in  eight  and  Erlicki's  in  three  days. 

Tellyesnicky's  Fluid. — This  solution  gives  better  nuclear  fixation 
than  Müller's  fluid. 

Potassium  bichromate 3  g™- 

Glacial  acetic  acid S  C-C- 

Water 100    " 

Small  pieces  of  tissue  remain  in  this  fluid  for  one  or  two  days. 
Larger  pieces  may  also  be  used,  but  require  a  longer  period  of  fixation. 
Wash  thoroughly  in  flowing  water.  Dehydrate  in  graded  alcohol, 
beginning  with  15%. 

Zenker's  Fluid. — 

Potassium  bichromate 2.5  gm. 

Sodium  sulphate I        '* 

Corrosive  sublimate 5        " 

Glacial  acetic  acid 5      ^•'^• 

Water 100       " 

It  is  advisable  to  add  the  glacial  acetic  acid  in  proper  proportion  to 
the  quantity  of  the  solution  to  be  used,  and  not  to  add  it  to  the  stock  solution. 
The  tissues  are  allowed  to  remain  for  from  six  to  twenty-four  hours  in  this 


INFILTRATION    AND    IMBEDDING.  2/ 

mixture,  in  which  they  float  for  a  short  time.  They  are  then  washed  in 
running  water  for  from  twelve  to  twenty-four  hours,  and  transferred  to 
gradually  concentrated  alcohols.  Crystals  of  sublimate  which  may  be 
present  are  removed  with  iodized  alcohol.  Zenker's  fluid  penetrates 
easily,  and  fixes  nuclear  and  protoplasmic  structures  equally  well  without 
decreasing  the  staining  qualities  of  the  elements. 

Formalin  (Formol). — Of  recent  years  formalin,  which  is  a 
40%  solution  of  the  gas  formaldehyd  in  water,  has  been  much  used  as  a 
fixing  fluid.  It  is  best  employed  in  the  form  of  a  solution  made  by  add- 
ing 10  parts  of  formalin  to  90  parts  of  water  or  normal  saline  solution. 
Small  pieces  of  tissue  remain  in  this  solution  for  from  twelve  to  twenty- 
four  hours,  larger  pieces  or  organs  a  number  of  days  or  weeks,  and  are 
then  transferred  to  90%  alcohol. 

Potassium  Bichromate  and  Formalin. — 

Potassium  bichromate,  2%  to  3%  aqueous 

solution 90  parts. 

Formalin I° 

Tissues  remain  in  this  fluid  from  several  days  to  several  weeks,  de- 
pending on  their  size.  Wash  thoroughly  in  water  and  dehydrate  in 
alcohol.     Useful  for  fixation  of  central  nervous  system. 

We  have  attempted  to  give  only  the  fixing  and  hardening  fluids  com- 
monly employed  for  general  purposes.  There  are  numerous  other  fluids 
used  for  special  purposes  ;  these  will  be  noticed  under  the  headings  of  the 
corresponding  tissues  and  organs. 

INFILTRATION  AND  IMBEDDING. 

Few  tissues  have  a  consistency,  even  after  fixation,  which  enables 
them  to  be  cut  into  sections  thin  enough  to  be  studied  under  high  magni- 
fication, without  being  especially  prepared  for  this  purpose.  To  admit 
of  sectioning,  it  is  generally  necessary  to  imbed  them  in  media  which 
off"er  no  resistance  to  the  knife,  while  giving  them  firmness,  and  do  not 
obscure  the  structure  of  the  sections  when  cut,  or  which  may  be  removed 
from  the  sections  by  methods  which  are  not  harmful  to  them.  The  media 
used  for  imbedding  may  be  classed  under  two  heads:  (i)  Such  as  are 
fluid  when  warm,  and  may  in  this  state  be  caused  to  penetrate  the  tissue, 
and  are  solid  when  cold  ;  (2)  such  as  are  fluid  when  in  solution,  and  m 
this  state  will  penetrate  tissues,  but  which  become  solid  on  the  evaporation 
of  the  solvent.  The  best  example  of  the  former  class  of  substances  is 
paraffin  ;  and  of  the  latter,  celloidin  (collodion  or  photoxylin). 

I.  PARAFFIN  IMBEDDING. 
In  describing  the  method  of  paraffin  infiltration  and  imbedding  it 
is  assumed  that  the  tissues  have  been  previously  fixed  and  hardened  and  are 
in  alcohol  ready  for  further  manipulation.  From  the  hardened  tissues 
small  flat  pieces  are  cut  with  a  sharp  knife  or  razor.  If  possible,  they 
should  be  square,  rectangular,  or  triangular  in  shape,  their  surfaces  not 
exceeding  Vz  square  inch,  and  their  thickness  from  yi  to  yi  of  an  inch. 
Pieces  of  larger  size  may  be  imbedded,  if  desired,  provided  the  requisite 
care  be  exercised.  The  pieces  selected  are  placed  in  absolute  alcohol,  m 
which  they  remain  until  thoroughly  dehydrated.     From  the  latter  they 


28  THE    MICROSCOPIC    PREPARATION. 

can  not  be  passed  directly  into  paraffin,  as  alcohol  dissolves  only  a  small 
percentage  of  paraffin,  and,  consequently,  the  preparation  would  not  be 
infiltrated  with  the  imbedding  mass.  The  pieces  of  tissue  are  therefore 
first  placed  in  some  fluid  which  mixes  with  absolute  alcohol  and  at  the 
same  time  dissolves  the  paraffin.  There  are  many  reagents  which  have 
this  property,  such  as  xylol,  toluol,  chloroform,  and  a  number  of  oils  (oil 
of  turpentine,  oil  of  cedar,  oil  of  origanum,  etc.).  Of  these  xylol  may 
be  recommended  for  general  use.  In  the  xylol  the  tissues  remain  for 
from  two  to  twelve  hours,  the  time  depending  somewhat  on  the  size  of 
the  pieces  and  on  the  density  of  the  tissue.  When  thoroughly  permeated 
by  the  xylol,  they  are  transparent.  From  the  xylol  (toluol,  chloroform, 
or  oils)  the  tissues  are  placed  in  melted  paraffin.  Two  kinds  of  paraffin 
are  generally  used,  one  having  a  melting  point  of  38°  to  40°  C. — soft 
paraffin — and  another  with  a  melting  point  of  50°  to  58°  C. — so-called 
hard  paraffin.  The  paraffin  should  always  be  filtered  before  using.  This 
is  best  done  by  using  a  hot -water  filter.  It  is  essential  that  melted 
paraffin  have  a  constant  temperature  while  the  tissues  are  being  infiltrated. 
This  is  attained  by  placing  the  receptacle  containing  the  paraffin  in  a 
paraffin  oven  regulated  by  means  of  a  thermostat  to  a  temperature  about 
two  degrees  above  the  melting  point  of  the  hard  paraffin. 

Filtered  hard  and  soft  paraffin  may  be  kept  in  suitable  glass  beakers 
in  respective  compartments  in  the  paraffin  oven.  After  the  tissues  are 
thoroughly  permeated  with  the  xylol,  this  is  poured  off  and  melted  soft 

paraffin  added,  and  the  dish  replaced 
in  the  paraffin  oven.  In  the  soft 
paraffin  the  tissues  remain  from  one  to 
four  hours,  at  the  end  of  which  time 
the  soft  paraffin  is  poured  off  and 
hard  paraffin  added,  and  the  dish 
again  placed  in  the  oven.  In  the 
hard  paraffin  the  tissues  remain  from 
Fig.  3.-B0X  for  imbedding  tissues.  two  to  twelve  hours,  depending  on  the 

size  of  the  pieces.  They  are  now 
ready  to  be  imbedded.  Two  metallic  L's  are  placed  together  on  a 
glass  or  metal  plate  in  such  a  way  as  to  make  a  rectangular  box. 
(Fig.  3.)  This  is  filled  with  melted  hard  paraffin  taken  from  the 
oven.  Before  the  paraffin  cools,  the  piece  of  tissue  to  be  imbedded 
is  taken  from  the  hard  paraffin  in  the  oven  and  placed  with  one 
of  its  flat  surfaces  against  one  end  of  the  box.  If  several  pieces  of 
tissue  are  to  be  imbedded,  a  piece  may  thus  be  placed  in  each  end  of 
the  box.  While  transferring  the  tissues  from  the  hard  paraffin  to  the 
imbedding  box  they  should  be  handled  with  forceps,  the  blades  of 
which  have  been  warmed  in  a  flame.  As  soon  as  the  paraffin  in  which 
the  tissues  are  imbedded  has  cooled  sufficiently  to  allow  the  formation  of 
a  film  over  the  melted  paraffin,  the  imbedding  box  is  placed  in  a  dish  of 
cold  water.  This  cools  the  paraffin  quickly  and  prevents  its  becoming 
brittle.  A  stay  of  from  five  to  ten  minutes  in  the  cold  water  hardens  the 
paraffin  so  that  the  L's  may  be  removed,  and  the  paraffin  block  containing 
the  imbedded  tissue  may  be  taken  from  the  plate.  It  is  well  to  place  the 
paraffin  block  thus  obtained  back  into  the  cold  water  for  a  short  time,  so 
that  it  may  become  hard  all  the  way  through.  As  the  paraffin  often 
adheres  closely  to  the  glass  or  metal  plate  and  the  L's,  it  is  advisable  to 
cover  these  parts  with  a  very  thin  layer  of  glycerin  before  imbedding. 
There  is  then  no  difficulty  in  separating  them  from  the  paraffin  block. 


INFILTRATION    AND    IMBEDDING.  29 

If  a  large  number  of  small  pieces  of  tissue  are  to  be  imbedded,  it 
is  often  more  convenient  to  imbed  them  in  a  small  flat  dish  of  suitable  size. 
The  dish  to  be  used  is  covered  on  its  inner  surface  with  a  thin  layer  of 
glycerin  and  partly  filled  with  hard  paraffin  and  the  several  pieces  of 
tissue  to  be  imbedded  transferred  to  it  and  arranged  on  the  bottom  of  the 
dish.  As  soon  as  a  film  forms  over  the  paraffin  the  dish  is  placed  care- 
fully in  cold  water  and  the  paraffin  allowed  to  harden.  The  large  piece 
of  paraffin  thus  obtained  may  then  be  cut  into  several  smaller  pieces, 
each  containing  a  piece  of  the  imbedded  tissue. 

On  transferring  an  object  from  one  fluid  into  another,  so-called 
curre?its  of  diffusion  occur,  which  produce,  especially  in  such  tissues  as 
contain  cavities,  shrinkage  and  tearing.  This  often  results  in  totally 
changing  the  finer  structure  of  the  tissues.  It  is  therefore  necessary  to 
proceed  with  greater  caution  than  in  the  method  above  indicated.  Mix- 
tures containing  different  percentages  of  alcohol  and  the  intermediate 
fluid  (xylol,  toluol,  chloroform)  may  be  prepared,  and  the  object,  ac- 
cording to  its  delicacy,  passed  through  a  greater  or  smaller  number  of 
such  solutions.  In  ordinary  cases  a  single  mixture  of  alcohol  and  the 
intermediate  fluid  is  sufficient,  the  object  remaining  in  the  solution  for  a 
length  of  time  varying  with  its  size  before  being  passed  into  the  pure  in- 
termediate fluid.  This  part  of  the  treatment  may  of  course  be  slowed  or 
hastened  according  to  the  number  of  such  mixtures,  each  succeeding  one 
containing  more  and  more  of  the  intermediate  fluid.  After  the  object 
has  been  passed  into  the  pure  intermediate  fluid  it  should  be  just  as  care- 
fully passed  into  the  infiltrating  fluid.  If  paraffin  is  to  be  used  and  the 
object  be  delicate,  the  following  method  is  advisable  :  The  object  is 
placed  in  a  glass  vessel  half  filled  with  the  intermediate  fluid,  into  which 
a  few  pieces  of  soft  paraffin  are  dropped.  The  vessel  is  then  covered 
and  allowed  to  remain  at  the  temperature  of  the  room.  "When  the 
paraffin  is  dissolved  the  cover  is  removed  and  the  vessel  placed  in  a  par- 
affin oven  kept  at  a  temperature  corresponding  to  the  melting  point  of 
the  paraffin.  The  volatile  intermediate  fluid  evaporates  gradually,  and 
in  a  few  hours  the  object  is  infiltrated  with  an  almost  pure  soft  paraffin. 
It  may  now  be  transferred  into  pure  melted  hard  paraffin.  In  this  the 
tissue  remains  for  a  longer  or  shorter  time,  according  to  its  size. 

It  is  often  of  advantage  to  infiltrate  the  tissues  in  a  pa7'tial  vacmmi. 
In  this  way  there  is  obtained  a  better  infiltration  of  the  tissues  with  the 
paraffin,  and  this  seems  to  obtain  a  better  consistency.  Especially  is 
this  method  to  be  recommended  in  imbedding  larger  embryos  or  tissue 
with  cavities.  A  simple  and  convenient  method  is  as  follows  :  a  glass 
bottle  of  suitable  size  is  warmed  and  partly  filled  with  melted  hard 
paraffin  and  placed  at  one  end  of  a  copper  plate,  the  other  end  of  which 
is  heated  by  a  flame,  care  being  taken  to  heat  the  copper  plate  only 
sufficiently  to  keep  melted  the  paraffin  in  the  bottle.  The  bottle  is  fitted 
with  a  rubber  cork  with  two  holes,  into  which  have  been  inserted  two  L" 
shaped  glass  tubes,  provided,  the  one  with  a  short  rubber  tube,  which  is 
clamped,  the  other  with  a  tube  of  sufficient  length  to  reach  to  a  Chapman 
water-pump.  The  tissues  are  placed  in  the  paraffin,  the  bottle  tightly 
corked,  and  the  water-pump  allowed  to  play  for  about  half  an  hour,  after 
which  the  tissues  are  imbedded  in  the  paraffin  used  during  this  procedure. 
High  temperatures  are,  as  a  rule,  injurious  to  tissues.  This 
should  always  be  borne  in  mind,  and  the  student  should  aim  to  keep  his 
specimens  at  the  lowest  possible  temperature  conducive  to  proper  infiltra- 
tion.    If  for  any  reason  higher  temperatures  become  necessary,  the  ex- 


so 


THE    MICROSCOPIC    PREPARATION. 


posure  of  the  tissues  to  their  action  should  be  as  brief  as  possible.  The 
paraffins  most  used  have  a  melting  point  of  40°  to  60°  C.  The  kind  of 
paraffin  used  should  depend  upon  the  temperature  of  the  room  in  which 
the  sectioning  is  to  be  done.  It  is  even  well  to  have  different  mixtures  of 
hard  and  soft  paraffins  at  hand,  so  that,  if  the  temperature  of  the  room 
be  low,  tissues  may  be  imbedded  in  a  softer  mixture,  and  vice  versa. 

The  process  of  infiltrating  and  imbedding  in  paraffin  is  repre- 
sented by  the  following  diagram  (instead  of  xylol,  other  intermediate 
fluids  may  be  used)  : 

Alcohol,  90% 

t 
Abs.  alcohol   

t 
Alcohol-xylol  mixture 

Xylol  <■ 

t 
Xylol-paraffin  (cold) 

t 
^Xylol-paraffin  (in  paraffin  oven) 

if 

Soft   paraffin  -s 

if 
Hard  paraffin 

t    . 
Imbedding 

The  size  and  density  of  the  tissues  must  necessarily  regulate  the 
length  of  time  necessary  for  their  proper  infiltration.  It  is  therefore  hardly 
possible  to  give  any  definite  figures.  In  presenting  the  following  table  we 
have  taken  as  a  standard  any  tissue  that  has  the  general  consistency  of 
liver  fixed  in  alcohol.  The  time  is  given  in  hours,  and  should  in  each 
case  be  regarded  as  a  minimum.  A  longer  stay  in  any  one  fluid  will, 
under  favorable  circumstances,  do  no  harm. 


Small  Ob- 
jects  UNDER. 
I  MM.  IN 

Diameter. 


Middle-sized 
Objects  up 

TO   5  MM.   IN 

Diameter. 


Large  Ob- 
jects UP  TO  10 

MM.  IN 

Diameter. 


Very  Large  Ob- 
jects, although 
NOT  More  than  a 

Few  cm.  in  Di- 
ameter. 


Absolute  alcohol 
Xylol 


From   now  on 

affin  oven  : 
Soft  paraffin    . 
Hard  paraffin 


in    par- 


I 


24 
6 


For  a  longer  or 
shorter  time  in 
the  fluids,  ac- 
cording to  the 
size  of  the  object. 


2.  CELLOIDIN. 

The  best  and  most  convenient  celloidin  to  use  in  microscopic  work  is 
Schering's  granular  celloidin,  put  up  in  i -ounce  bottles.  Of  this  a 
stock  or  thick  solution  is  prepared  by  dissolving  6  gm.  of  the  celloidin  in 
100  c.c.  of  equal  parts  of  absolute  alcohol  and  ether.  Of  this,  when 
required,  a  thin  solution  is  prepared  by  diluting  a  quantity  of  the  stock 
solution  with  an  equal  quantity  of  the  ether  and  alcohol  solution. 


INFILTRATION    AND    IMBEDDING.  3  I 

The  hardened  tissues  are  cut  into  small  pieces,  which  should  not 
be  much  more  than  ^  of  an  inch  in  thickness  and  not  have  a  surface 
area  of  more  than  3^  of  a  square  inch.  Much  larger  pieces  of  tissue 
may  be  imbedded  in  celloidin.  This  is  not  advised,  however,  unless  it  is 
necessary  to  show  the  whole  of  the  structure  to  be  studied.  The  pieces 
to  be  imbedded  are  placed  for  twenty-four  hours  in  absolute  alcohol,  and  are 
then  transferred  for  twenty-four  hours  to  a  mixture  of  equal  parts  of  abso- 
ute  alcohol  and  ether.  Then  they  go  into  the  thin  celloidin  solution,  where 
they  remain  for  from  twenty-four  hours  to  several  days,  depending  on  the 
size  and  density  of  the  pieces  to  be  imbedded.  The  pieces  of  tissue  are 
then  transferred  to  the  thick  celloidin  solution,  where  they  again  remain 
for  from  twenty-four  hours  to  several  days.  If  it  is  desired  to  imbed  large 
pieces,  especially  if  these  be  of  the  medulla  or  brain,  the  stay  in  the  cel- 
loidin solutions  should  be  lengthened  to  several  weeks.  The  hardening 
of  the  celloidin  may  now  be  obtained  by  one  of  several  methods. 

A  sufficient  quantity  of  the  stock  or  thick  celloidin  solution  to 
cover  well  the  tissues  to  be  imbedded  is  poured  into  a  flat  dish  large 
enough  to  allow  the  pieces  to  be  imbedded  to  be  arranged  on  its  bottom 
and  leave  a  space  of  about  ^  of  an  inch  between  adjacent  pieces.  The 
dish  is  then  covered,  not  too  tightly,  and  set  aside  to  allow  the  ether  and 
alcohol  to  evaporate.  In  one  or  two  days  the  celloidin  is  usually  hard 
enough  to  cut  into  small  blocks,  each  block  containing  a  piece  of  the 
imbedded  tissue.  The  blocks  of  celloidin  are  now  further  hardened  by 
placing  them  in  80^  alcohol.  A  stay  of  several  hours  in  this  alcohol  is 
usually  sufficient  to  give  them  the  hardness  required  for  section  cutting. 
After  the  celloidin  pieces  have  obtained  the  right  degree  of  hardness  they 
are  to  be  stuck  to  small  pieces  of  pine  wood  or  vulcanized  fiber  so  that  they 
may  be  clamped  into  the  microtome.  This  is  done  in  the  following  way  : 
A  piece  of  celloidin  containing  a  piece  of  tissue  is  trimmed  with  a  sharp 
knife  so  that  only  a  rim  of  celloidin  about  ^  of  an  inch  in  thickness 
surrounds  the  piece  of  tissue.  It  is  now  placed  for  a  few  moments  in  the 
ether  and  alcohol  solution.  This  is  to  soften  the  surfaces  of  the  celloidin. 
One  end  of  a  small  pine-wood  or  vulcanized-fiber  block  about  one  inch  long, 
the  cut  end  of  which  has  a  surface  area  slightly  larger  than  the  celloidin 
block,  is  dipped  for  a  few  moments  into  the  ether  and  alcohol  solution  and 
then  into  the  thick  celloidin.  The  celloidin  block  is  now  taken  from  the 
ether  and  alcohol  solution,  dipped  into  the  celloidin,  and  pressed  against 
the  end  of  the  wooden  or  vulcanized-fiber  block,  which  has  been  coated 
with  the  celloidin.  The  whole  is  now  set  aside  for  a  little  while  to  allow 
the  celloidin  to  harden  slightly,  and  is  then  placed  in  80 1^  alcohol.  In 
the  alcohol  it  may  remain  indefinitely ;  it  may,  however,  be  used  for 
cutting  as  soon  as  it  again  becomes  hard. 

The  piece  of  tissue  to  be  imbedded  may  be  mounted  at  once  on 
pine-wood  or  vulcanized-fiber  blocks  from  the  thick  celloidin  solution  by 
pouring  a  small  amount  of  thick  celloidin  over  one  end  of  the  block  and 
placing  the  piece  of  tissue  from  the  thick  celloidin  solution  onto  the  layer 
of  celloidin  on  the  block.  In  three  to  four  minutes  a  layer  of  the  thick 
celloidin  solution  is  poured  over  the  piece  of  tissue  and  the  end  of  the 
block.  It  may  be  necessary  to  do  this  several  times  if  the  piece  of  tissue 
is  large  or  of  irregular  shape.  The  block  is  now  set  aside  for  about  five 
minutes,  and  is  then  placed  in  80%  alcohol,  where  it  remains  until  the 
celloidin  is  hard,  or  until  it  is  desired  to  cut  sections. 


32  THE    MICROSCOPIC    PREPARATION, 

The  tissues  may  be  imbedded  by  pouring  the  thick  cellojdin,  to- 
gether with  the  objects,  into  a  small  box  made  of  paper.  The  surface  of  the 
celloidin  hardens  in  about  an  hour  (preliminary  hardening),  after  which 
the  whole  is  transferred  to  80^  alcohol,  in  which  the  final  hardening 
takes  place.  The  paper  is  then  removed,  the  block  of  celloidin  trimmed 
to  a  convenient  size  and  fastened  on  a  block. 

While  being  cut,  celloidin  preparations  are  kept  moistened  with  80^ 
alcohol.  Organs  consisting  of  tissues  of  varying  consistency,  as  well 
as  very  dense  objects,  can  be  cut  with  better  results  in  celloidin  than  in 
paraffin.  On  the  other  hand,  celloidin  sections  can  never  be  cut  as  thin 
as  paraffin  sections,  and  the  after-treatment  (see  below),  fixation  on  the 
slide,  etc.,  are  much  more  complicated  than  in  the  case  of  paraffin  sec- 
tions. 

The  following  is  a  diagram  showing  the  process  of  infiltration 
and  imbedding  in  celloidin. 

gofo  alcohol 

t 
Abs.  alcohol 

t 
Abs.  alcohol  and  ether  (in  equal  parts) 

t 
Thin  celloidin  solution 

t 
Thick  celloidin  solution 

t_ 
Imbedding 

t 
80%  alcohol 

3.  CELLOIDIN-PARAFFIN. 

To  combine  the  advantages  which  infiltration  in  celloidin  and  in 
parafiin  offer,  a  method  of  celloidin-paraffin  infiltration  is  recommended. 
Preparations  that  have  been  imbedded  in  celloidin  or  photoxylin  and 
hardened  in  80^  alcohol  are  placed  for  about  twelve  hours  in  90%  alco- 
hol, from  which  they  are  transferred  to  a  mixture  of  equal  parts  of  oil  of 
origanum  and  gofo  alcohol.  They  are  then  immersed  for  a  short  time  in 
pure  origanum  oil,  then  in  a  mixture  of  equal  parts  of  origanum  oil  and 
xylol,  and  finally  in  pure  xylol.  From  this  point  the  regular  method 
of  infiltrating  with  paraffin  is  followed,  care  being  taken  that  the  pieces  re- 
main for  as  short  a  time  as  possible  in  the  different  fluids,  in  order  that 
the  celloidin  may  not  become  brittle. 

Very  thin  sections  may  be  obtained  by  painting  the  cut  surface  with 
a  thin  layer  of  a  very  dilute  celloidin  solution.  This  hardens  and  gives 
the  tissue  a  greater  consistency.  This  treatment  is  useful  in  the  combined 
celloidin-paraffin  method,  as  well  as  when  paraffin  alone  is  used. 


THE  MICROTOME  AND  SECTIONING. 

Instruments  known  as  microtomes  have  been  devised  in  order  that 
section  cutting  may  be  rendered  as  independent  as  possible  of  the  skill 
of  the  individual,  but  more  especially  to  obtain  series  of  sections  of  uni- 
form thickness.     Their  construction  varies  greatly.     Some  of  these  in- 


THE    MICROTOME    AND    SECTIONING.  33 

struments,  as  the  so-called  rocking  microtomes,  are  so  specialized  that  they 
only  cut  paraffin  objects  when  the  knife  is  transversely  placed.  Others 
have  a  more  general  function,  celloidin  as  well  as  paraffin  objects  being 
sectioned  with  the  knife  in  any  position.  To  the  latter  class  belong  the 
sliding  microtomes. 

In  figure  4  is  shown  an  instrument  which  may  be  recommended 
for  general  laboratory  work.  This  instrument  consists  of  a  horizontal 
base  which  rests  on  the  table,  and  a  vertical  plate  (a),  and  a  slide  (/>)  which 
supports  a  block  (c),  to  which  is  fastened  a  knife  by  means  of  a  thumb- 
screw (ä).  On  the  other  side  of  the  vertical  plate  is  a  metal  frame  (e), 
into  which  are  fastened  the  paraffin  and  celloidin  blocks  ;  this  frame  is 
attached  to  a  slide  (/),  which  may  be  elevated  or  lowered  by  a  feed  (  g) . 
This  feed  consists  of  a  micrometer  screw  acting  on  the  lower  surface 
of  the  slide.  The  micrometer  screw  is  provided  with  a  milled  head, 
divided  into  a  definite  number   of  parts   which   bear   a    definite  rela- 


Odp-^^ 

^^wr***' ' " ""  '*''^*"-w>'«p^pp^*^^^äÄäS=--n 

^^^^^^^^W^a 

^^■i 

J^5^ 

^wf-<* 

^^--.-.^J^ 

■'^*''^*C 

z^ 

Fig.  4. — Laboratory  microtome. 

tion  to  the  pitch  of  the  micrometer  screw.  The  instrument  shown 
in  the  figure  is  further  provided  with  a  lever  (//),  which  may  be 
so  adjusted  as  to  move  the  milled  head  on  the  micrometer  screw 
I  or  any  given  number  of  notches  at  each  movement  of  the  lever ; 
and  as  each  notch  on  the  milled  head  has  a  value  of  5  microns 
(■ooVt  °f  ^^  inch),  every  time  the  milled  head  is  moved  i  notch 
(toward  the  manipulator)  the  slide  carrying  the  clamp  holding  the  tissue 
is  elevated  5  microns ;  2  notches  would  elevate  the  tissue  10  microns 
(tsW  o^  ^^  inch)  ;  4  notches,  20  microns  (jaTiF  °^  ^^  inch),  etc.  It 
is  not  essential  to  have  a  lever  attached  to  the  instrument  as  above 
described,  although  this  is  very  convenient ;  if  not  present,  the  milled 
head  is  moved  the  desired  number  of  notches  with  the  hand. 

Minot  has  recently  devised  two  kinds  of  microtomes  which  deserve  spe- 
cial mention,  and  are  especially  to  be  recommended  for  accurate  work. 
One  of  these  (see  Fig.  5)  is  known  as  the  "Precision  Microtome."     It 
consists  of  a  square  frame  made  of  cast-iron,  to  which  the  knife  is  fastened, 
3 


Fig.  5- — Minot  automatic  precision  microtome. 


Fig.  6. — Minot  automatic  rotary  microtome. 
34 


THE    MICROTOME    AND    SECTIONING.  35 

Beneath  the  frame  which  supports  the  knife  are  two  horizontal  ways,  upon 
which  runs  the  sliding  carriage  supporting  an  adjustable  object-carrier. 
The  object  is  raised  by  a  micrometer  screw,  fed  automatically  by  a  large- 
toothed  wheel  attached  to  the  bottom  of  the  screw.  Both  paraffin  and 
celloidin  sections  may  be  cut  with  this  instrument.  The  other  type  of  mi- 
crotome is  known  as  the  ''New  Rotary  Microtome."  In  this  instrument 
(see  Fig.  6)  the  knife  is  carried  by  two  upright  standards  which  can  be 
adjusted  as  to  their  distance  from  the  object.  The  object,  which  needs 
to  be  imbedded  in  paraffin,  is  fixed  to  an  object-carrier,  which  may  be 
adjusted  to  any  plane,  and  which  is  fixed  to  a  vertical  carriage,  held  by 
adjustable  gibs  against  the  vertical  ways,  and  which  is  raised  or  lowered 
by  a  crank,  working  in  a  slide,  and  attached  to  an  axle  turned  by  the 
wheel.  The  vertical  carriage  also  carries  the  micrometer  screw,  to  which 
is  attached  a  toothed  wheel ;  this  is  turned  by  a  pawl  which  acts  upon  it. 
This  instrument  may  be  most  highly  recommended  for  the  cutting  of 
serial  sections. 

In  cutting  paraffin  sections  with  the  sliding  microtome  the 
knife  is  placed  at  an  angle  of  about  35°  to  40°  to  the  horizontal  plate  of 
the  microtome.  Sections  are  cut  more  easily  with  the  knife  in  this  posi- 
tion than  when  the  knife  is  placed  at  right  angles  to  the  microtome,  as  is 
often  recommended,  and  it  does  not  seem  that  the  tissues  suffer  materially 
from  distortion  when  they  are  cut  with  the  knife  at  an  angle,  as  is  some- 
times claimed. 

Before  fastening  the  paraffin  blocks  into  the  clamp  on  the  microtome, 
preparatory  to  cutting  sections,  the  paraffin  is  trimmed  with  a  sharp  knife 
from  the  end  of  the  paraffin  block  until  the  tissue  is  nearly  exposed,  care 
being  taken,  however,  to  leave  a  flat  surface.  The  top  of  the  paraffin 
block  is  then  beveled  off  on  three  sides  to  within  a  very  short  distance 
of  the  tissue.  The  fourth  side,  that  which  faces  the  knife  when  the  block 
is  clamped  in  the  microtome,  should  be  trimmed  only  to  within  about  /g  of 
an  inch  of  the  tissue.  This  edge  of  paraffin  is  made  use  of,  as  will  be  seen 
in  a  moment,  for  preventing  the  sections  from  curling  while  they  are  being 
cut.  The  paraffin  block  is  now  ready  to  be  clamped  in  the  microtome. 
This  is  done  in  such  a  way  that  the  paraffin  block  just  escapes  the  knife 
when  drawn  over  it.  A  number  of  rather  thick  sections  (20  to  40 
microns)  are  cut  by  moving  the  micrometer  screw  from  right  to  left  4 
to  8  notches  every  time  the  knife  has  been  drawn  over  the  paraffin 
block  and  has  been  brought  back  again,  until  it  is  noticed  that  the  knife 
touches  all  parts  of  the  top  of  the  paraffin  block,  or  until  the  tissue  is 
fairly  exposed.  (In  this  description  reference  is  made  to  the  simple  labora- 
tory microtome  shown  in  Fig.  4. )  The  succeeding  sections  may  now  be 
kept.  It  may  perhaps  be  well  to  state  that  it  is  better  not  to  try  to  cut 
very  thin  sections  at  the  beginning;  sections  15  to  20  microns  in  thickness 
will  answer  very  well.  To  begin  with,  then,  the  milled  head  of  the  mi- 
crometer screw  is  turned  4  notches  from  left  to  right,  and  the  knife  is 
drawn  over  the  block  with  a  steady,  even  pull,  and  without  using  undue 
pressure.  Usually  the  sections  will  curl  up  as  they  are  being  severed  from 
the  parafiin  block.  This  may  very  readily  be  prevented  by  holding  the 
tip  of  a  camel's -hair  brush,  which  has  been  pointed  by  drawing  it  between 
the  lips,  against  the  edge  of  the  section  as  soon  as  it  begins  to  curl.  A 
litde  practice  will  enable  one  to  do  this  almost  automatically.  The 
sections  are  transferred  to  paper  by  means  of  the  camel 's-hair  brush, 
which  process  is  facilitated  if  the  brush  has  been  slightly  moistened  with 
saliva,  as  the  section  will  then  adhere  lightly  to  the  brush. 


36  THE    MICROSCOPIC    PREPARATION. 

If  the  tissues  are  well  imbedded  and  not  too  hard,  and  if  the  knife 
is  sharp  and  properly  adjusted,  paraffin  sections  may  be  cut  in  such  a  way 
that  each  succeeding  section  adheres  to  the  preceding  one,  so  that  actual 
ribbons  of  paraffin  sections  may  be  made.  In  order  to  do  this,  the  knife 
should  be  at  right  angles  to  the  microtome.  The  paraffin  block  should  be 
trimmed  in  such  a  way  that  when  clamped  in  the  microtome  ready  for 
cutting  sections,  the  surface  of  the  paraffin  block  facing  the  knife  should 
be  exactly  parallel  to  its  edge,  also  to  the  opposite  side  of  the  block.  In 
other  words,  2  sides  of  the  paraffin  block  should  be  parallel  to  each 
other  and  to  the  knife  ;  then  if  the  paraffin  is  of  the  right  consistency, 
which  must  be  ascertained  by  trying,  the  sections  as  they  are  cut  will  ad- 
here to  each  other  and  form  a  ribbon.  If  the  sections  do  not -adhere  to 
each  other  it  is  quite  probable  that  the  paraffin  is  a  little  too  hard.  This 
may  often  be  remedied  by  holding  an  old  knife  or  other  metallic  instru- 
ment which  has  been  heated  in  a  flame  near  the  two  parallel  surfaces  for  a 
few  moments.  Care  should  be  taken  not  to  allow  this  instrument  to  touch 
the  paraffin.  This  is  a  very  convenient  and  rapid  way  of  cutting  par- 
affin sections.  To  facilitate  the  cutting  of  a  paraffin  possessing  a  rela- 
tively low  melting  point  in  a  room  with  a  high  temperature,  the  cooled 
knife  of  Stoss  may  be  used.  This  is  so  made  that  a  stream  of  ice -water 
may  be  passed  through  a  tube  running  through  the  entire  length  of  the 
back  of  the  blade.  Paraffin  sections  may  be  cut  in  ribbons — serial  sec- 
tions— on  an  ordinary  sliding  microtome;  for  this  purpose,  however,  the 
"automatic  rotary  microtome"  of  Minot  is  especially  recommended. 

Celloidin  Sections. — Before  fastening  the  block  of  wood  or  vul- 
canized fiber  to  which  the  celloidin  blocks  have  been  fixed  in  the  clamp 
on  the  microtome,  the  celloidin  should  be  trimmed  with  a  sharp  knife 
from  the  top  of  the  block  until  the  tissue  is  nearly  exposed,  care  being 
taken  to  leave  a  flat  surface.  The  sides  of  the  celloidin  block  are  then 
trimmed  down,  if  necessary,  to  within  about  Jg-  of  an  inch  of  the  tissue. 
The  block  is  now  clamped  in  the  microtome  at  such  a  level  that  it  just 
escapes  the  knife  when  drawn  over  it.  The  knife  is  placed  at  an  angle  of 
about  45°,  or  at  even  a  greater  angle.  During  the  process  of  cutting,  the 
knife,  as  also  the  tissue,  must  be  kept  constantly  moistened  with  80^ 
alcohol.  This  is  perhaps  most  easily  accomplished  by  taking  up  the  80 1^ 
alcohol  with  a  rather  large  camel' s-hair  brush  and  dipping  this  on  the 
celloidin  block  and  on  the  knife.  A  number  of  rather  thick  sections  are 
cut  until  the  knife  touches  the  entire  surface  of  the  block  or  until  the  tis- 
sue is  well  exposed.  The  sections  may  now  be  kept.  The  block  is  raised 
20  to  15  microns,  and  the  knife,  which  should  be  well  moistened  with 
80%  alcohol,  is  drawn  over  the  block  with  a  steady  pull,  not  with  a 
jerk.  The  sections  are  transferred  from  the  knife  to  distilled  water. 
This  is  perhaps  most  conveniently  done  by  placing  the  ball  of  one  of  the 
fingers  of  the  left  hand  under  the  edge  of  the  knife,  in  front  of  the  sec- 
tion, and  drawing  the  section  down  onto  the  finger  with  the  camel' s-hair 
brush.  The  finger  is  then  dipped  into  the  distilled  water  when  the  sec- 
tion floats  off.  If  the  sections  can  not  be  stained  within  a  few  hours  after 
they  are  cut,  they  are  best  transferred  to  a  dish  containing  80^  alcohol, 
in  which  they  may  be  left  until  it  is  desired  to  stain  them. 

The  sliding  microtomes  may  be  provided  with  an  arrangement  for  freez- 
ing tissues — a  so-called  freezing  apparatus.  This  consists  of  a  metal 
plate  on  which  the  tissue  is  laid;  an  ether  or  rigolene  atomizer  plays  upon 
its  lower  surface,  cooling  and  finally  freezing  the  object,  which  is  then  cut. 


THE    MICROTOME    AND    SECTIONING. 


17 


A  drop  of  fluid  (physiologic  saline  solution,  water,  etc.)  is  placed  upon 
the  knife,  in  which  the  section  thaws  out  and  spreads.  A  better  and 
more  rapid  method  of  freezing  tissues  consists  in  the  use  of  compressed 
carbon  dioxid,  as  recommended  by  Mixter.  Cylinders  containing  about 
twenty  pounds  of  the  liquid  gas  may  be  obtained  from  Bausch  &  Lomb, 
who  also  make  a  small  microtome  designed  for  this  purpose.  In  figure  7 
is  shown  the  lower  third  of  a  cylinder  for  compressed  carbon  dioxid 
firmly  fastened  to  a  thick  board,  and  connected  by  means  of  a  short  piece 
of  strong  rubber  tubing  with  the  freezing  box  of  the  microtome.  The 
handle  of  the  escape  valve  is  from  8  to  10  inches  long,  so  that  the 
quantity  of  escaping  gas  may  be  readily  controlled.  The  pieces  of  tis- 
sue are  placed  on  the  freezing  box  of  the  microtome  and  the  escape  valve 
slowly  opened  until  a  small  quantity  of  the  gas  escapes.  Small  pieces  of 
tissue  are  frozen  in  about  thirty  seconds  to  a  minute  ;  tissues  taken  from 
alcohol  should  be  washed  for  a  short  time  in  running  water  before  freez- 
ing. A  strong  razor  may  be  used  for  cutting  sections  ;  or  better,  a  well- 
sharpened  blade  of  a  carpenter's  plane,  as  suggested  by  Mallory  and 
Wright.  Sections  are  transferred  to  distilled  water  or  normal  salt  solu- 
tion, and  if  fixed  may  be  stained  at  once.  Sections  of  fresh  tissue 
should  be  taken  from  the  normal  salt  solution  and  transferred  to  a  fixing 
fluid. 

Bardeen  has  devised  a  microtome  to  be  used  with  compressed  carbon 
dioxid,  which  presents  many  advantages.  It  admits  of  better  control  of 
the  temperature  of  the  freezing  stage  and  there  is  less  carbon  dioxid  wasted 
than  with  other  instruments  of  this  type.  It  freezes  almost  instantane- 
ously, since  the  expanding  carbon  dioxid  is  caused  to  pass  through  a 
spiral  passage  contained  in  the  freezing  chamber.  In  this  apparatus  the 
microtome  is  attached  to  the  steel  cylinder  containing  the  carbon  dioxid. 
It  is  impossible  to  cut  thin  sections  with  a  knife  that  is  not  sharp, 
or  with  one  that  is  nicked.  A  few  directions  as  to  sharpening  a  micro= 
tome  knife  may  therefore  not  be  out  of  place.     For  this  purpose  a  good 


Fig.   7. — Apparatus  for  cutting  tissues  frozen  by  carbon  dioxid. 


Belgian  hone  is  used,  which  should  be  moistened  or  lubricated  with  filtered 
kerosene  oil  or  with  soap  as  necessity  demands.  While  sharpening  the 
knife  it  is  grasped  with  both  hands — with  one  by  the  handle,  with  the 


38 


THE    MICROSCOPIC    PREPARATION. 


Other  by  the  end.  The  hone  is  placed  on  a  table  with  one  end  directed 
toward  the  person  sharpening.  If  the  knife  is  very  dull,  it  is  ground  for 
some  time  on  the  concave  side  only  (all  microtome  knives  are  practically 
plane  on  one  side  and  concave  on  the  other),  with  the  knife  at  right 
angles  to  the  stone.  It  is  carried  from  one  end  of  the  stone  to  the  other, 
edge  foremost,  giving  it  at  the  same  time  a  diagonal  movement,  so  that 
with  each  sweep  the  entire  edge  is  touched  (see  Fig.  8).  In  drawing 
back  the  knife,  the  edge  is  slightly  raised.  The  knife  is  ground  on  the 
concave  side  until  a  fine  thread  (feather  edge)  appears  along  the  entire 
edge.  It  is  then  ground  on  both  sides,  care  being  taken  to  keep  the  knife 
at  right  angles  to  the  stone,  to  keep  it  flat,  and  to  use  practically  no  pres- 
sure. It  is  a  good  plan  to  turn  the  knife  on  its  back  when  the  end  of  the 
stone  is  reached.  On  the  return  stroke,  the  knife  is  again  held  at  right 
angles  to  the  stone,  the  same  diagonal  sweep  is  used  (see  Fig.  8),  so  that  the 
whole  edge  of  the  knife  is  touched  with  each  sweep.  The  grinding  on 
both  sides  is  continued  until  the  thread  above  mentioned  has  disappeared. 
The  knife  should  now  be  carefully  cleaned  and  stropped,  with  the  back  of 
the  knife  drawn  foremost.  The  strop  should  be  flat  and  rest  on  a  firm 
surface. 


Fig.  8. — Diagram  showing  direction  of  the  movements  in  honing. 


THE  FURTHER  TREATMENT  OF  THE  SECTION. 

U  FLXATION  TO  THE  SLIDE  AND  REMOVAL  OF  PARAFFIN. 

Sections  obtained  by  means  of  the  microtome  undergo  further  treat- 
ment either  loose  or,  better,  fixed  to  a  slide  or  cover-glass,  thus  making 
further  manipulation  much  easier. 

The  simplest,  surest,  and  most  convenient  method  of  fixing  par- 
affin sections  to  the  slide  is  by  means  of  the  glycerin=albumen  of  P. 
Mayer  (83.2).      Egg-albumen  is  filtered  and  an  equal  volume  of  glycerin 


THE    FURTHER    TREATMENT    OF    THE    SECTION.  39 

added.  To  prevent  decomposition  of  the  fluid  a  little  camphor  or  sodium 
salicylate  is  placed  in  the  mixture.  A  drop  of  this  fluid  is  smeared  on  the 
slide  or  cover-slip  as  evenly  and  thinly  as  possible.  A  section  or  a  series 
of  sections  arranged  in  their  proper  sequence  is  then  placed  upon  the  slide 
so  prepared.  Any  folds  in  the  section  are  smoothed  out  with  a  brush,  and 
the  section  or  the  whole  series  gently  pressed  down  upon  the  glass.  When 
the  desired  number  of  sections  are  on  the  slide  or  cover-slip,  they  are 
warmed  over  a  small  spirit  or  gas  flame  until  the  paraffin  is  melted.  At 
the  same  time  the  albumen -coagulates.  The  sections  are  now  fixed,  and 
are  loosened  from  the  glass  only  when  agents  are  used  which  dissolve 
albumen,  as,  for  instance,  strong  acids,  alkalies,  and  certain  staining 
fluids.  If  it  is  desired  that  a  given  space,  say  the  size  of  a  cover-slip,  be 
filled  up  with  sections  as  far  as  possible,  an  outline  of  the  cover-slip  to  be 
used  may  be  drawn  upon  a  piece  of  paper  and  placed  under  the  slide  in 
the  required  position. 

A  second  and  in  many  respects  better  method  is  the  fixation  of 
the  section  with  distilled  water  (Gaule).  The  paraffin  sections  are 
spread  in  proper  sequence  on  a  thin  layer  of  water  placed  on  the  slide. 
There  should  be  sufficient  water  to  float  the  sections.  The  slide  is  then 
dried  in  a  warm  oven  kept  at  30°  to  35°  C,  or  gently  heated  by  holding 
it  at  some  distance  from  a  spirit  or  gas  flame  (the  paraffin  should  not 
melt).  By  this  treatment  the  sections  are  entirely  flattened  out.  The 
superfluous  water  is  either  drained  off"  by  tilting  or  drawn  off  with  blot- 
ting-paper, the  sections  are  definitely  arranged  with  a  brush,  and  the 
whole  is  placed  for  several  hours  in  a  warm  oven  at  30°  to  35°  C.  The 
sections  thus  dried  are  exposed,  over  a  flame,  to  a  temperature  higher 
than  the  melting  point  of  the  paraffin,  and  from  now  on  can  be  subjected 
to  almost  any  after-treatment.  The  slide  or  cover-slip  should  be  thor- 
oughly cleaned  (preferably  with  alcohol  and  ether),  as  otherwise  the  water 
does  not  remain  in  a  layer,  but  gathers  in  drops. 

The  advantage  of  this  method  lies  in  the  fact  that  the  evaporated 
water  can  have  no  possible  influence  on  the  subsequent  staining  of  the 
sections,  while  albumen,  especially  if  it  be  in  a  thick  layer,  is  sometimes 
stained,  thus  diminishing  the  transparency  of  the  preparation. 

This  method,  although  trustworthy  for  alcohol  and  sublimate  prepara- 
tions, often  fails  with  objects  that  have  been  treated  with  osmic  acid, 
chromic  acid  and  its  mixtures,  nitric  acid,  and  picrosulphuric  acid.  In 
such  cases  advantage  may  be  taken  of  the  so-called  Japanese  method, 
which  is  a  combination  of  the  above  fixation  methods.  A  little  Mayer's 
albumen  is  placed  on  the  slide  and  so  spread  about  that  hardly  a  trace  of 
the  substance  can  be  seen.  The  slide  is  then  put  in  a  warm  oven  heated 
to  70°  C.  This  temperature  soon  coagulates  the  albumen,  after  which 
the  sections  are  fixed  to  the  slide  by  the  water  method  (Rainke,  95). 
The  procedure  can  be  varied  by  adding  to  the  distilled  water  one  drop  of 
glycerin-albumen  or  gum  arable  to  every  30  c.c.  of  water  {vi J.  also 
Nussbaum). 

When  a  large  number  of  paraffin  sections  are  to  be  fixed  to  cover-slips, 
the  following  method  may  be  recommended  :  A  small  porcelain  evapo- 
rating dish  is  nearly  filled  with  distilled  water  and  placed  on  a  stand 
which  elevates  it  6  to  8  inches  from  the  table.  A  number  of  sec- 
tions are  placed  on  the  water,  which  is  then  heated  by  means  of  a  gas 
flame  until  the  sections  become  perfectly  flat,  care  being  taken  not  to 
raise  the  temperature  of  the  water  sufficiently  to  melt  the  paraffin.     Each 


40  THE    MICROSCOPIC    PREPARATION. 

section  is  then  taken  up  on  a  cover-slip  coated  with  a  very  thin  layer  of 
Mayer's  albumen  fixative.  During  this  procedure  the  cover-slips  are  held 
by  forceps,  and  the  sections  are  guided  by  means  of  a  small  camel's-hair 
brush.  When  all  the  sections  have  thus  been  placed  on  cover-slips  they 
are  placed  for  four  to  six  hours  in  a  warm  oven  maintained  at  30°  to 
35°  C. 

Removal  of  Paraffin. — Before  paraffin  sections,  either  fixed  or 
loose,  are  subjected  to  further  manipulation,  the  paraffin  surrounding  the 
tissues  must  be  removed.  This  may  be  done  by  means  of  several  agents 
having  a  solvent  action  on  paraffin,  such  as  xylol,  toluol,  oil  of  turpen- 
tine, etc.  After  the  paraffin  has  been  dissolved,  the  sections  are  trans- 
ferred to  absolute  alcohol  and  by  this  means  prepared  for  further  treatment 
with  aqueous  or  weak  alcoholic  solutions. 

Dextrin  Method  of  fixing  Paraffin  Sections. — This  method  is 
to  be  recommended  for  class-room  purposes  where  30  to  50,  or  even 
tnore  sections  need  to  be  stained  at  one  time. 

The  following  solutions  are  kept  on  hand : 

Sohttlon  I : 

A  solution  of    equal    parts  of    white  sugar 

and  boiling  distilled  water     .  300  c.c. 

A  solution  of  equal  parts  of  distilled  water 

and  dextrin 100    " 

Absolute  alcohol       200    " 

Mix  the  sugar  and  dextrin  solutions  in  a  mortar,  and  add  very  slowly, 
while  constantly  stirring,  the  absolute  alcohol  ;  filter  through  fine  muslin. 
Keep  in  a  wide-mouthed  bottle  through  the  cork  of  which  there  has  been 
placed  a  broad  camel's-hair  brush. 

Solution  2  : 

Photoxylin 10  gm. 

Absolute  alcohol 100  c.c. 

Ether 500    " 

The  sections  to  be  stained  are  cut  and  arranged  on  a  clean  piece  of 
paper.  A  clean  glass  plate  is  coated  with  a  thin  layer  of  solution  No.  i. 
The  sections  are  arranged  on  this  and  pressed  against  the  plate  with  the 
finger.  The  plate  is  now  placed  in  a  warm  oven  (temperature  40°  C), 
where  it  remains  for  several  hours.  The  plate  is  then  warmed  over  a 
flame  until  the  paraffin  of  the  sections  begins  to  melt  and  is  then  placed 
in  a  tray  containing  xylol,  where  it  remains  until  the  paraffin  is  dissolved. 
It  is  then  transferred  to  a  tray  containing  95^  alcohol  and  the  xylol  re- 
moved. The  plate  is  next  taken  from  the  tray  and  the  alcohol  drained 
off.  The  plate  is  now  covered  with  a  thin  layer  of  solution  No.  2,  and 
set  aside,  at  an  angle,  until  the  photoxylin  dries.  The  plate  is  now 
placed  in  the  staining  fluid,  in  which,  or  in  the  water  used  in  washing  off 
the  staining  fluid,  the  thin  layer  of  photoxylin,  to  which  the  sections  ad- 
here, separates  from  the  plate.  This  thin  film  may  now  be  treated  as 
one  section  and  carried  on  in  this  form  through  the  several  stages  of 
staining  and  clearing  until  the  process  is  completed.  The  individual 
sections  are  cut  from  the  film  with  scissors. 

Celloidin  preparations  can  not  be  fixed  to  the  slide  with  the 
same  degree  of  certainty,  although  many  sections  may  be  treated  at  one 
time.  The  celloidin  sections  can  be  collected  in  their  sequence  on  strips 
of  paper  by  gently  pressing  such  a  strip,  on  the  blade  of  a  knife,  onto  the 


STAINING.  41 

section  floating  in  the  alcohol.  The  sections  adhere  to  the  paper,  and  in 
this  way  the  entire  surface  of  the  strip  may  be  covered  by  series  of  sections. 
To  prevent  the  drying  of  the  sections,  a  number  of  such  strips  are  laid 
in  rows  on  a  layer  of  blotting-paper  moistened  with  70%  alcohol.  A  glass 
plate  of  corresponding  size  is  painted  with  very  fluid  celloidin.  After  the 
layer  of  celloidin  is  dry,  the  strips  of  paper  are  laid,  one  by  one,  on  the 
glass  plate,  with  sections  downward,  and  the  fingers  gently  passed  over 
the  reverse  side.  This  process  is  continued  until  the  entire  surface  of 
the  glass  is  covered.  On  carefully  raising  the  strips  it  is  seen  that  the 
sections  will  adhere  to  the  layer  of  celloidin.  (To  prevent  drying, 
sections  must  be  kept  moistened  with  70%  alcohol.)  After  first  drying 
the  sections  with  blotting-paper,  a  second  layer  of  very  thin  celloidin  is 
painted  on  the  surface  of  the  glass  plate.  When  this  layer  is  also  dry, 
the  plate  with  its  adherent  sections  is  placed  in  water.  Here  the  double 
layer  of  celloidin  containing  the  sections  is  separated  from  the  glass,  and 
is  ready  for  further  manipulation.  Before  mounting,  the  sheet  of  celloidin 
is  cut  with  scissors  into  convenient  portions. 

In  the  case  of  celloidin  sections,  if  it  be  desirable  to  preserve 
the  surrounding  celloidin,  care  should  be  taken  that  the  preparations 
should  not  come  in  contact  with  any  agents  dissolving  celloidin.  These 
latterare  alcohols  from  95%  upward,  ether,  several  ethereal  oils,  especially 
oil  of  cloves,  but  not  the  oils  of  origanum,  cedar  wood,  lavender,  etc. 

2.  STAINING. 

It  is  in  most  cases  necessary  to  stain  tissues  to  bring  clearly  to  view 
the  tissue  elements  and  their  relation  to  each  other.  The  purpose  of 
staining  is  therefore  to  differentiate  the  tissue  elements.  The  differential 
staining  is  due  to  the  fact  that  certain  parts  of  the  tissue  take  up  more  stain 
than  others.  Staining  of  sections  may  be  looked  upon  as  a  microchemic 
color  reaction,  and  has  therefore  a  value  beyond  the  mere  coloring  of 
sections  so  that  they  may  be  seen  more  clearly. 

Broadly  speaking,  stains  used  in  microscopic  work  may  be  divided 
into  basic  stains,  which  show  special  affinity  for  the  nuclei  of  cells  and  are 
therefore  known  as  nuclear  stains,  and  acid  stains,  which  color  more 
readily  the  protoplasm — protoplasmic  stains.  Certain  stains,  which  we 
may  know  as  selective  stains  (they  maybe  either  basic  or  acid),  color  one 
tissue  element  more  vividly  than  others,  or  to  the  exclusion  of  others. 
Since  the  various  tissue  elements  show  affinity  for  different  stains,  prepa- 
rations may  be  colored  with  more  than  one  stain.  Accordingly  we  have 
simple,  double,  triple,  and  multiple  staining. 

Certain  stains  are  also  especially  adapted  for  staining  in  bulk  or  mass 
— that  is,  staining  a  piece  of  tissue  before  it  is  sectioned. 

SECTION  STAINING. 
Carmin. — Aqueous  Borax=carmin  Solution. — 8  gm.  of  borax 
and  2  gm.  of  carmin  are  ground  together  and  added  to  150  c.c. 
of  water.  After  twenty-four  hours  the  fluid  is  poured  off  and  filtered. 
The  sections,  pVeviously  freed  from  paraffin  and  treated  with  alcohol,  are 
placed  in  this  fluid  for  several  hours  (as  long  as  twelve),  and  then  washed 
out  in  a  solution  of  0.5  to  1%  hydrochloric  acid  in  70%  alcohol. 
They  are  then  transferred  to  70%  alcohol. 

Alcoholic    Borax=carmin    Solution. — 3  gm.   of  carmin  and 


42  THE    MICROSCOPIC    PREPARATION. 

4.  gm.  of  borax  are  placed  in  93  c.c.  of  water,  after  which  100  c.c.  of 
70^  alcohol  is  added.  The  mixture  is  stirred,  then  allowed  to  settle, 
and  later  filtered.  Sections  are  treated  as  in  the  aqueous  borax-carmin 
solution. 

Paracarmin  is  the  carmin  stain  containing  the  most  alcohol, 
and  is  therefore  of  great  value. 

Carminic   acid I       gm. 

Aluminium  chlorid 0.5     " 

Calcium  chlorid 4        " 

Alcohol,  70% 100      c.c. 

Paracarmin  stains  quickly,  is  not  liable  to  overstain,  and  is  there- 
fore peculiarly  adapted  to  the  staining  of  large  objects.  Specimens  are 
washed  in  70^  alcohol,  with  the  addition  of  0.5^  aluminium  chlorid 
or  2.5^  glacial  acetic  acid  in  case  of  overstaining  (P.  Mayer,  92). 

Czocor's  Cochineal  Solution. — 7  gm.  of  powdered  cochineal 
and  7  gm.  of  roasted  alum  are  kept  suspended  in  100  c.c.  of  water  by 
stirring  while  the  mixture  is  boiled  down  to  half  its  volume.  After 
cooling  it  is  filtered  and  a  little  carbolic  acid  added.  This  fluid  stains 
quite  rapidly  and  does  not  overstain.  Before  the  sections  are  placed  in 
alcohol  they  should  be  washed  with  distilled  water,  as  otherwise  the  alum 
is  precipitated  on  the  section  by  the  alcohol. 

Partsch  recommends  the  following  solution  of  cochineal :  Finely  pow- 
dered cochineal  is  boiled  for  some  time  in  a  5^  aqueous  solution  of 
alum,  and  filtered  on  cooling,  after  which  a  trace  of  hydrochloric  acid  is 
added.     It  stains  sections  in  two  to  five  minutes. 

Alum-carmin  (Grenacher). — 100  c.c.  of  a  3%  to  5%  solution 
of  ordinary  alum,  or  preferably  ammonia -alum,  are  mixed  with  o.  5  gm.  to  i 
gm.  of  carmin,  boiled  for  one-fourth  of  an  hour,  and  after  cooling  filtered 
and  enough  distilled  water  added  to  replace  that  lost  by  evaporation.  This 
fluid  stains  quickly  but  does  not  overstain.     Wash  the  sections  in  water. 

Hematoxylin. — Böhmer's  Hematoxylin  : 

Hematoxylin  crystals I  gm. 

Absolute  alcohol 10  c.c. 

Potassium  alum 10  gm. 

Distilled  water 200  c.c. 

Dissolve  the  hematoxylin  crystals  in  the  alcohol,  and  the  alum  in  the  distilled  water. 
While  constantly  stirring,  add  the  first  solution  to  the  second. 

The  whole  is  then  left  for  about  fourteen  days  in  an  open  jar  or  dish  pro- 
tected from  the  dust,  during  which  time  the  color  changes  from  violet  to 
blue.  After  filtering,  the  stain  is  ready  for  use.  Sections,  either  loose  or 
fixed  to  the  slide  or  cover-slip,  are  placed  in  this  solution,  and  after  about 
half  an  hour  are  washed  with  water.  If  the  nuclei  are  well  stained  the  further 
treatment  with  alcohol  may  be  commenced.  Should  the  sections  be  over- 
stained,  a  condition  showing  itself  in  the  staining  of  the  cell -protoplasm 
as  well  as  the  nuclei,  the  sections  are  then  washed  in  an  acid  alcohol  wash 
(six  to  ten  drops  of  hydrochloric  acid  to  100  c.c.  of  70^  alcohol)  until 
the  blue  color  has  changed  to  a  reddish -brown  and  very  little  stain  comes 
from  the  section — usually  about  one  to  two  minutes.  They  are  then 
washed  in  tap -water,  and  passed  into  distilled  water  before  placing  in 
alcohol. 


STAINING. 


43 


Delafield's  Hematoxylin : 


Hematoxj'lin  crystals 4  gm. 

Absolute  alcohol 25  c.c. 

Ammonia  alum,  saturated  aqueous  solution  400   " 

Alcohol,  g^fo 100   " 

Glycerin '    .  100  " 

Dissolve  hematoxylin  crystals  in  absolute  alcohol  and  add  to  the  alum  solution,  after 
which  place  in  an  open  vessel  for  four  days,  filter,  and  add  the  95%  alcohol  and  glycerin. 

After  a  few  days  it  is  again  filtered.  This  fluid  is  either  used  pure  or 
diluted  Avith  distilled  water.  Staining  is  the  same  as  with  Böhmer' s  hema- 
toxylin. 

Friedländer's  Qlycerin=hematoxylin : 

Hematoxylin  crystals 2  gm. 

Potassium  alum       2    " 

Absolute  alcohol 100  c.c. 

Distilled  water loo    " 

Glycerin 100    " 

Dissolve  the  hematoxylin  crj'stals  in  the  absolute  alcohol  and  the  alum  in  the  water ; 
Ti-iiv  the  two  solutions  and  add  the  glycerin. 

The  mixture  is  filtered  and  exposed  for  several  weeks  to  the  air  and 
light,  until  the  odor  of  alcohol  has  disappeared,  and  then  again  filtered. 
It  stains  very  quickly.  Sections  are  afterward  washed  in  water  and  are 
placed  for  a  short  time  in  acid  alcohol  if  the  nuclei  are  to  be  especially 
brought  out. 

Ehrlich's  Hematoxylin : 

Hematoxylin  crystals 2  gm. 

Absolute  alcohol 60  c.c. 

Glycerin  "I     saturated  with    ....  60    " 

Distilled  water  J    ammonia  alum 60    " 

Glacial  acetic  acid 3     " 

The  solution  is  to  be  exposed  to  light  for  a  long  time.  It  is  ready  for  use  when  it 
acquires  a  deep-red  color. 

Stain  as  above. 

Hemalum  (P.  Mayer,  91). — i  gm.  of  hematein  is  dissolved 
by  heating  in  50  c.c.  of  absolute  alcohol.  This  is  poured  into  a  solu- 
tion of  50  gm.  of  alum  in  i  liter  of  distilled  water  and  the  whole  well 
stirred.  A  thymol  crystal  is  added  to  prevent  the  growth  of  fungus. 
The  advantages  of  hemalum  are  as  follows  :  The  stain  may  be  used  im- 
mediately ,  after  its  preparation,  it  stains  quickly,  never  overstains, 
especially  when  diluted  with  water,  and  penetrates  deeply,  making  it 
useful  for  staining  in  bulk.  After  staining,  sections  or  tissues  are  washed 
in  distilled  water. 

Acid  Hemalum. — To  the  above  hemalum  solution  is  added  2(/c  of 
glacial  acetic  acid.  Stains  even  more  rapidly  than  hemalum,  and  gives 
excellent  nuclear  differentiation.      Wash  sections  in  tap-water. 

Heidenhain's  Iron  Hematoxylin. — Good  results,  particu- 
larly in  emphasizing  certain  structures  of  the  cell  (centrosome),  are  ob- 
tained by  the  use  of  M.  Heidenhain's  iron  hematoxylin  (92.  2).  Tissues 
are  fixed  in  saline  sublimate  solutions,  alcohol,  or  Carnoy's  fluid.  A^ery 
thin  sections  (in  case  of  amniota  not  over  4/1)  are  fixed  to  the  slide  with 
water  and  put  into  a  2.5^  aqueous  solution  of  ammonium  sulphate  of 
iron  for  four  to  eight  hours  (not  longer).  After  careful  rinsing  in  Avater, 
the  sections  are  brought  into  a  solution  of  hematoxylin  prepared  as  fol- 
lows :      Hematoxylin  crystals   i   gm.,  absolute  alcohol   10  c.c,  and  dis- 


44  THE    MICROSCOPIC    PREPARATION. 

tilled  water  90  c.c.  This  solution  should  remain  in  an  open  vessel  foi 
about  four  weeks,  and,  before  using,  should  be  diluted  with  an  equal 
volume  of  distilled  water.  Staining  takes  place  in  twelve  to  twenty-four 
hours,  after  which  the  sections  are  rinsed  in  tap-water  and  again  placed 
in  a  like  solution  of  ammonium  sulphate  of  iron,  until  black  clouds  cease 
to  be  given  off  from  the  sections.  They  are  rinsed  in  distilled  water, 
passed  through  alcohol  into  xylol,  and  mounted  in  balsam.  Should  a 
protoplasmic  stain  be  desired,  rubin  in  weak  acid  solution  may  be 
employed. 

Coal=tar  or  anilin  stains. — Ehrlich  classifies  all  anilin  stains  as  salts 
having  basic  or  acid  properties.  The  basic  anilin  stains,  such  as  safra- 
nin,  methylene-blue,  methyl-green,  gentian  violet,  methyl-violet,  Bis- 
marck brown,  thionin,  and  toluidin-blue  are  nuclear  stains,  while  the 
acid  anilin  stains,  such  as  eosin,  erythrosin,  benzopurpurin,  acid  fuchsin, 
lichtgrün,  aurantia,  orange  G,  and  nigrosin  stain  diffusely  and  are  used  as 
protoplasmic  stains. 
Safranin  : 

Safranin I  gm. 

Absolute  alcohol 10  c.c. 

Anilin  water  .    .     • 90  " 

Anilin  water  is  prepared  by  shaking  up  5  c.c.  to  8  c.c.  of  anilin  oil  in  lOO  c.c.  of 
distilled  water  and  filtering  through  a  wet  filter.  Dissolve  the  safranin  in  the  anilin 
water  and  add  the  alcohol.     Filter  before  using. 

Stain  sections  of  tissues  fixed  in  Flemming's  or  Hermann's  solutions 
for  twenty -four  hours,  and  decolorize  with  a  weak  solution  of  hydrochloric 
acid  in  absolute  alcohol  (i  :  1000).  After  a  varying  period  of  time  (usu- 
ally only  a  few  minutes)  all  the  tissue  elements  will  be  found  to  have 
become  bleached,  only  the  chromatin  of  the  nucleus  retaining  the  color. 

Bismarck  Brown. — ^A  very  convenient  color  to  handle  is 
Bismarck  brown.  Of  this,  i  gm.  is  boiled  in  100  c.c.  of  water,  filtered, 
and  yi  of  its  volume  of  absolute  alcohol  added.  Bismarck  brown  stains 
quickly  without  overstaining,  and  is  also  a  purely  nuclear  stain.  Wash 
in  absolute  alcohol. 

MethyUgreen  stains  very  quickly  (minutes),  i  gm.  is  dis- 
solved in  100  c.c.  of  distilled  water  to  which  25  c.c.  of  absolute  alcohol 
is  added.  Rinse  sections  in  water,  then  place  for  a  few  minutes  in  70^ 
alcohol,  transfer  to  absolute  alcohol  for  a  minute,  etc. 

Other  so-called  basic  anilin  stains  can  be  used  in  a  similar 
manner.  Thionin  or  toluidin-blue  in  dilute  aqueous  solution?  are  espe- 
cially useful.      Nuclei  appear  blue  and  mucus  red. 

Double  Staining.: — When  certain  stains  are  used  in  mixtures 
or  in  succession,  all  portions  of  the  section  are  not  stained  alike,  but 
certain  elements  take  up  one  stain,  others  another.  This  elective  affin- 
ity of  tissues  is  taken  advantage  of  in  plural  staining.  If  two  stains  are 
employed,  one  speaks  of  double  staining. 

Picrocarmin  of  Ranvier. — Two  solutions  are  prepared,  a  satu- 
rated aqueous  solution  of  picric  acid  and  a  solution  of  carmin  in  ammonia. 
The  second  is  added  to  the  first  to  the  point  of  saturation.  The  whole  is 
evaporated  to  one-fifth  of  its  volume  and  filtered  after  cooling.  The 
solution  thus  obtained  is  again  evaporated  until  the  picrocarmin  remains 
in  the  form  of  a  powder.  A  i  ^  solution  of  the  latter  in  distilled  water 
is  the  fluid  used  for  staining. 


STAINING.  45 

To  Stain  with  this  sokition,  one  or  two  drops  are  placed  on  the  slide 
over  the  object  and  the  Avhole  put  in  a  moist  chamBer  for  twenty-four 
hours.  A  cover-slip  is  then  placed  over  the  preparation,  the  picrocarmin 
drained  off  with  a  piece  of  blotting-paper,  and  a  drop  of  formic-glycerin 
(i  :  loo)  brought  under  the  cover-slip  by  irrigation.  Proper  differentia- 
tion takes  place  only  after  a  few  days,  and  the  acid-glycerin  may  then  be 
replaced  by  the  pure  glycerin.  In  objects  fixed  with  osmic  acid,  the 
nuclei  appear  red,  connective  tissue  pink,  elastic  fibers  canary  yellow, 
muscle  tissue  straw  color,  keratohyalin  red,  etc. 

Weigert's  Picrocarmin. — The  preparation  of  Weigert's  picro- 
carmin is  somewhat  simpler.  2  gm.  of  carmin  are  stirred  in  4  c.c. 
of  ammonia  and  allowed  to  remain  standing  in  a  well -corked  bottle 
for  twenty -four  hours.  This  is  mixed  with  200  c.c.  of  a  concentrated 
aqueous  solution  of  picric  acid  to  which  a  few  drops  of  acetic  acid  are 
added  after  another  twenty-four  hours.  The  result  is  a  slight  precipitate 
that  does  not  dissolve  on  stirring.  Filter  after  twenty-four  hours.  Should 
the  precipitate  also  pass  through  the  filter,  a  little  ammonia  is  added  to  dis- 
solve it.  Both  picrocarmin  solutions  dissolve  off  sections  fixed  to  the  slide 
with  albumen. 

Carmin=bleu  de  Lyon  (of  Rose). — Sections  or  pieces  of  tis- 
sue are  first  stained  with  carmin  (alum-  or  borax-carmin).  Bleu  de  Lyon 
is  dissolved  in  absolute  alcohol  and  diluted  with  the  latter  until  the  solu- 
tion is  of  a  light  bluish  color.  In  this  the  sections  or  pieces  of  tissue  are 
after-stained  for  twenty-four  hours  (developing  bone  stains,  for  instance, 
blue). 

Picric  acid  is  often  used  as  a  secondary  stain,  either  in  aque- 
ous (saturated  solution  diluted  i  to  3  times  in  water)  or  in  alco- 
holic solution  (weak  solutions  in  70-^0,  80%,  and  absolute  alcohol). 
Sections  previously  treated  with  carmin  or  hematoxylin  are  stained  for 
two  to  five  minutes,  washed  in  water  or  alcohol,  and  transferred  to  abso- 
lute alcohol,  etc.  Sections  stained  in  safranin  can  be  exposed  to  the  ac- 
tion of  an  alcoholic  picric  acid  solution.  A  solution  of  picric  acid  in 
70%  alcohol  may  be  used  to  wash  sections  stained  in  borax-carmin. 
This  often  gives  a  good  double  stain.  Sections  can  also  be  first  treated 
with  picric  acid  and  afterward  stained  with  alum-carmin. 

Hematoxylin. — Van  Qieson's  Acid  fuchsin=picric  acid  Solu= 

tion. Stain  in  any  one  of  the  hematoxylin  solutions  and  after  rinsing 

sections  in  water  counter-stain  in  the  following : 

Acid  fuchsin,  1%  aqueous  solution  ....       5  c.c. 
Picric  acid,  saturated  aqueous  solution      .    .  loo    " 

Dilute  with  an  equal  quantity  of  distilled  water  before  using.  The 
hematoxylin  stained  sections  remain  in  the  solution  for  from  one  to  two 
minutes,  are  then  rinsed  in  water,  dehydrated  and  cleared. 

Hematoxylin=eosin. — Sections  already  stained  in  hematoxylin 
are  placed  for  two  to  five  minutes  in  a  i  %  to  2  %  aqueous  solution  of 
eosin  or  in  a  1%  solution  of  eosin  in  60^  alcohol.  They  are  then 
washed  in  water  until  no  more  stain  comes  away,  after  which  they  remain 
for  only  a  short  time  in  absolute  alcohol.  In  place  of  the  eosin  solution 
a  I  %  aqueous  solution  of  benzopurpurin  may  be  used  or  the  following 
solution  of  erythrosin  (Held)  : 

Erythrosin I  gm- 

Distilled  water        150  c.c. 

Glacial  acetic  acid 3  drops. 


46  THE    MICROSCOPIC    PREPARATION. 

Hematoxylin-safranin  of  Rabl  (85). — Sections  of  preparations 
fixed  with  chromic -formic  acid  or  with  a  solution  of  platinum  chlorid  are 
stained  for  a  short  time  with  Delafield's  hematoxylin,  then  counterstained 
for  twelve  to  twenty-four  hours  with  safranin  and  washed  with  absolute 
alcohol  until  no  more  color  is  given  off. 

Biondi'-Heidenhain  Triple  Stain. — Of  the  many  triple  stains  in 
use  we  mention  only  the  most  important,  the  rubin  S — orange  G — 
methyl-green  mixture  of  Ehrlich  and  Biondi,  employed  according  to  the 
modification  of  M.  Heidenhain.  The  best  results  are  obtained  with  ob- 
jects fixed  in  saline  sublimate  solution.  The  three  stains  just  mentioned 
are  prepared  in  concentrated  aqueous  solutions.  (In  100  c.c.  of  distilled 
water  there  are  dissolved  respectively  about  20  gm.  of  rubin  S,  and  8 
gm.  of  orange  G  and  methyl-green.)  These  concentrated  solutions  are 
combined  in  the  following  proportions:  rubin  S  4,  orange  G  7,  methyl- 
green  8.  The  stock  solution  thus  obtained  is  diluted  with  50  to  100 
times  its  volume  of  distilled  water  before  using.  The  sections  should  be 
as  thin  as  possible  and  fixed  to  the  slide  by  the  water  method.  They 
remain  for  twenty-four  hours  in  the  stain,  and  are  then  rinsed  in  distilled 
water  or  in  90^  alcohol  or  in  such  with  the  addition  of  a  little  acetic  acid 
(i  to  2  drops  to  50  c.c).  Before  staining  it  is  occasionally  of  advantage 
to  treat  the  sections  with  acetic  acid  (2  :  1000)  for  one  to  two  hours. 

STAINING  IN  BULK. 

Instead  of  staining  in  sections,  entire  objects  can  be  stained  before 
cutting.  This  method  is  in  general  much  slower,  and  demands,  there- 
fore, special  staining  solutions,  as,  for  instance  : 

Alcoholic  Bo7'ax-car7nin  Solution. — Pieces  ^  cm.  in  diameter  remain 
in  the  stain  at  least  twenty-four  hours,  are  then  decolorized  for  the  same 
length  of  time  in  acid  alcohol  (0.5%  to  1%  hydrochloric  acid  in  70^ 
alcohol),  and  after  washing  in  70 '^  alcohol  are  transferred  to  90^  alco- 
hol.     Larger  objects  require  a  correspondingly  longer  time. 

Paracai'inin. — Treatment  as  in  section  staining-  length  of  time 
according  to  size  of  object. 

Ahim-carmin  of  Grenacher. — This  never  overstains.  Time  of  stain- 
ing according  to  size  of  object.  Wash  in  water,  then  transfer  to  70^ 
and  90^  alcohol. 

Hemalum,  when  diluted  with  water,  is  very  useful  for  staining  in  bulk. 
After  staining,  objects  should  be  washed  with  distilled  water. 

Böhmer' s  hematoxylin  stains  small  pieces  very  sharply.  Use  the  same 
as  hemalum. 

Hematoxylin  staining  according  to  R.  Heidenhain's  method  is 
especially  recommended  for  staining  in  bulk. 

Stain  objects  fixed  in  alcohol  or  picric  acid  twenty-four  hours  in  a 
0.33'^  aqueous  solution  of  hematoxylin  ;  transfer  for  an  equal  length  of 
time  to  a  0.51^  aqueous  solution  of  potassium  Chromate,  changing  often 
until  the  color  ceases  to  run.  Wash  with  water  and  pass  into  strong 
alcohol.  This  stain  also  colors  the  protoplasm,  and  is  so  powerful  that 
very  thin  sections  are  an  absolute  condition  to  the  clearness  of  the  prepa- 
ration. 

If  the  objects  have  been  fixed  with  picric  acid  and  the  latter  has 
not  been  entirely  washed  out,  staining  in  bulk  by  the  above  methods  pro- 
duces very  striking  differentiation. 


METHODS    OF    IMPREGNATION. 


47 


Pieces  of  tissue  stained  in  bulk  may  be  infiltrated,  imbedded, 
and  cut  according  to  the  ordinary  methods.  Under  these  circumstances, 
section  staining  is  not  necessary  unless  a  still  further  differentiation  be 
desired. 

In  general,  then,  the  treatment  of  the  object  is  somewhat  as  fol- 
lows :  First,  it  is  fixed  in  some  one  of  the  fixing  fluids  already  described, 
then  carefully  washed,  and  in  certain  cases  stained  in  bulk  before  infiltrat- 
ing with  paraffin  or  celloidin  ;  or  the  staining  may  be  postponed  until 
the  tissue  has  been  cut.  In  the  latter  case,  the  sections  are  subjected  to 
the  stain  either  loose  or  fastened  to  the  slide  or  cover-slip. 

In  all  cases  it  is  absolutely  essential  that  the  paraffin  be  entirely 
removed.  After  the  sections  have  been  stained  and  washed,  they  are 
transferred  to  absolute  alcohol  in  case  it  be  desired  to  mount  them  in 
some  resinous  medium.  They  may  also  be  mounted  in  glycerin  or 
acetate  of  potash,  into  which  they  may  be  passed  directly  from  distilled 
water. 

The  method  of  staining  tissues  in  sections  or  in  bulk  is  shown  in 
the  following  diagrams : 


In  Bulk. 
90%  alcohol 


Water 


In  Sections. 
Celloidin  sections      Paraffin  sections 
in  90  %  alcohol  I 

Remove  paraffin 

t 
Absolute  alcohol 

t 
90%  alcohol 

H 


Distilled 
water 


Wash  in  water       Wash  in  acid  alcohol 


t 
70^  alcohol 


t 
70^  alcohol 


•  Distilled  v/ater 


Stain 


Absolute  alcohol 


Wash  in  Wash  in  acid 

water  alcohol 

4.  .\ 

Alcohol  Alcohol 


Absolute  alcohol 


METHODS  OF  IMPREGNATION. 

The  impregnation  methods  differ  from  the  staining  methods  in  that 
in  the  latter  the  coloration  is  obtained  by  reagents  in  solution,  while  in 
the  former  the  tissues  are  filled  with  fine  particles  which  enter  into  com- 
bination with  certain  constituents  of  the  tissue  elements  and  are  reduced 
in  them. 

Silver  Nitrate  Method. — This  method  was  suggested  by  Krause ; 
it  was,  however,  brought  to  prominence  by  v.  Recklinghausen.  It  is 
especially  useful  for  staining  the  intercellular  substances  of  epithelium, 
endothelium,  and  mesothelium  and  the  ground-substance  of  connective 


48  THE    MICROSCOPIC    PREPARATION. 

tissues.  The  method  may  be  used  on  fresh  tissues  or  on  fixed  tissues  ; 
the  employment  of  fresh  tissue  is,  however,  more  satisfactory.  The  tis- 
sues to  be  impregnated  are  spread  in  thin  layers,  and  immersed  in  a 
0.5^  to  i^  solution  of  silver  nitrate  for  from  ten  to  fifteen  minutes; 
they  are  then  rinsed  in  distilled  water  and  placed  in  fresh  distilled  water 
or  70^  alcohol  or  a  4%  solution  of  formalin  and  exposed  to  direct  sun- 
light, where  they  remain  until  they  assume  a  brown  color.  The  sunlight 
reduces  the  silver,  in  the  form  of  fine  particles  which  appear  black  on 
being  examined  with  transmitted  light.  The  preparations  thus  obtained 
may  be  examined  in  glycerin  or  dehydrated  and  mounted  in  balsam. 
(See  methods  of  injection  for  staining  the  endothelial  cells  of  blood  and 
lymph  vessels. ) 

Gold  Chlorid  Method. — In  gold  chlorid  impregnation  the  cells  and 
fibers  of  certain  tissues  are  stained  while  the  intercellular  substances  remain 
uncolored.  The  coloration  is  obtained  by  a  reduction  of  the  gold  (either 
by  sunlight  or  certain  reagents — formic  acid,  acetic  acid,  citric  acid,  oxalic 
acid),  in  the  form  of  very  fine  particles  which  impart  to  the  tissues  a  pur- 
plish-red color.  This  method  is  especially  useful  for  bringing  to  view  the 
terminations  of  nerve-fibers,  both  motor  and  sensory  ;  however,  it  may  also 
be  employed  for  staining  other  tissue  elements.  The  method  of  gold 
impregnation  was  introduced  by  Cohnheim  and  was  used  by  him  in 
staining  the  nerve  terminations  in  the  cornea.  It  has  received  numerous 
modifications  since  its  introduction.     The  following  may  be  mentioned  : 

Cohnheim'' s  Method. — Small  pieces  of  muscle  are  placed  in  a  i  ^ 
solution  of  gold  chlorid  acidulated  by  a  trace  of  acetic  acid.  In  this 
they  become  yellow  (in  from  a  few  minutes  to  half  an  hour).  They  are 
then  rinsed  in  distilled  water,  placed  in  water  slightly  acidulated  with 
acetic  acid,  and  kept  in  the  dark.  As  a  rule,  the  pieces  will  change  in 
color,  becoming  yellowish-gray,  grayish- violet,  and  finally  red,  from  one 
to  three  days  generally  being  required  for  this  process.  The  parts  best 
adapted  to  examination  are  those  in  the  transitional  stage  of  violet  to  red. 
This  procedure  has  been  subjected  to  innumerable  modifications ; 
of  these,  the  most  used  are  :  ( i )  The  method  of  Löwit :  Small  pieces  are 
placed  in  a  solution  of  i  vol.  formic  acid  and  2  vols,  distilled  water 
until  they  have  become  transparent  (ten  minutes).  They  are  then  placed 
in  a  I  ^  solution  of  gold  chlorid,  in  which  they  become  yellow  (one-quarter 
hour).  They  are  now  again  placed  in  formic  acid,  in  which  they 
pass  through  the  same  color  changes  as  above.  Finally,  they  are  washed 
and  teased,  or  subsequently  treated  with  alcohol  and  cut.  (2)  Kühne 
(86)  acidifies  with  0.5^  solution  of  acetic  acid  (especially  in  the  case  of- 
muscle),  then  treats  the  specimens  with  a  i^  solution  of  gold  chlorid, 
and  reduces  the  gold  with  20  to  25%  formic  acid  dissolved  in  equal  parts 
of  water  and  glycerin.  (3)  Ranvier  (89)  acidifies  with  fresh  lemon  juice 
filtered  through  flannel,  then  treats  with  a  i  %  solution  of  gold  chlorid 
(quarter  of  an  hour  or  longer),  and  finally  either  places  the  specimen  iu 
water  acidulated  with  acetic  acid  (i  drop  to  30  c.c.  water)  and  subjects 
it  to  light  for  one  or  two  days,  or  reduces  it  in  the  dark,  as  in 
Löwit' s  method,  in  a  solution  of  i  vol.  formic  acid  and  2  vols,  water. 
(4)  Gerlach  uses  the  double  chlorid  of  gold  and  potassium,  but  in  weaker 
concentrations  than  a  i  ^  solution,  otherwise  he  continues  as  in  the 
method  of  Cohnheim.  (5)  Golgi  (94)  also  uses  the  same  double  chlorid, 
but  acidifies  with  0.51^  arsenious  acid,  and  then  reduces  in  i  ^  arseni- 
ous  acid  in  the  sunlight. 


METHODS    OF    IMPREGNATION.  49 

QoIgi'sChromsilver  or  Chromsublimate  Method. — This  method 
depends  on  the  formation  of  a  very  fine  precipitate,  which  forms  in  cer- 
tain tissue  elements  or  in  preexisting  spaces,  when  treated  first  with  a 
solution  of  bichromate  of  potassium  and  secondarily  with  a  solution  of 
silver  nitrate  or  bichlorid  of  mercury.  The  nature  and  precise  location 
of  this  precipitate  is  not  well  understood.  It  is  very  probable,  however, 
as  Kallius  suggests,  that  an  albumin -chromsilver  compound,  of  an 
unknown  constitution,  is  formed  in  the  cells  and  processes  or  in  spaces 
filled  with  the  precipitate.  This  method  is  especially  useful  in  bringing 
to  view  the  cellular  elements  of  the  nervous  system,  both  central  and 
peripheral  ;  further,  the  end-ramifications  of  gland  ducts,  and  now  and 
then  cell  boundaries.  Usually  only  a  small  percentage  of  the  tissue 
elements  or  the  spaces  of  any  given  tissue  are  colored.  This  may,  how- 
ever, be  regarded  as  one  of  the  advantages  of  the  method,  since  it 
enables  a  clearer  view  of  the  parts  colored.  The  precipitate  appears 
black  in  transmitted  light.  It  is  necessary  to  state,  however,  that  this 
method  is  very  unreliable,  and  that  failures  are  often  met  with,  also  that 
an  amorphous  precipitate  is  generally  formed,  both  in  and  about  the 
tissues,  which  in  part  at  least  destroys  the  usefulness  of  the  preparations 
obtained. 

Golgi's  methods  will  perhaps  be  better  understood  if  we  first 
give  a  short  historic  sketch  of  their  development. 

In  the  year  1875  Golgi  applied  his  method  as  follows :  He  fixed  (olfacton'  bulb)  in 
Müller' s  fluid,  and  increased  the  percentage  of  bichromate  on  changing  the  fluid  (up  to 
4  ^).  Fixation  lasted  five  or  six  weeks  in  summer  and  three  or  four  months  or  more 
in  winter.  He  then  took  out  pieces  of  the  tissue  every  four  or  five  days  and  treated  them 
experimentally  with  a  0.5^  to  ifc  silver  nitrate  solution.  In  summer  this  process  took 
about  twenty-four  hours,  and  in  winter  forty-eight  hours,  although  a  longer  treatment 
was  not  found  to  be  detrimental.  This  method  must  be  regarded  as  veiy  uncertain,  since 
the  length  of  time  during  which  the  specimens  remain  in  Müller' s  fluid  must  be  very 
closely  calculated,  as  it  depends  largely  upon  the  temperature  of  the  medium.  As  soon 
as  the  silver  reaction  was  established,  the  pieces  were  preserved  either  in  the  silver  solu- 
tion itself  or  in  alcohol.  The  sections  were  finally  washed  in  absolute  alcohol,  cleared 
with  creosote,  and  mounted  in  Canada  balsam.  The  impregnation  disappeared  in  a 
short  time.  In  the  year  1885  Golgi  made  a  further  announcement  regarding  his  method, 
recommending  for  fixation  the  pure  bichromate  of  potassium,  as  well  as  Müller' s  fluid. 
Pieces  of  the  brain  and  spinal  cord  (from  I  to  I.5  c.c.  in  size)  from  a  freshly  killed  ani- 
mal were  used,  and  the  reaction  sometimes  took  place  in  from  twenty-four  to  forty-eight 
hours  after  death.  For  fixing,  potassium  bichromate  solution  in  gradually  ascending 
strengths  (l^  to  5^)  was  employed,  large  amounts  of  the  fluid  being  used  and  placed 
in  well-sealed  receptacles.  The  fluid  was  repeatedly  changed,  and  camphor  or  salicylic 
acid  was  added  in  order  to  prevent  the  growth  of  fungi.  Since  it  is  difficult  to  determine 
exactly  when  fixation  in  potassium  bichromate  reaches  the  precise  point  favorable  to  sub- 
sequent treatment  with  nitrate  of  silver,  because  the  process  depends  entirely  upon  the 
temperature  and  quantity  of  the  fluid,  it  becomes  necessary,  after  about  six  weeks'  treat- 
ment with  the  bichromate,  to  experiment  every  eight  days  or  so  to  see  whether  the 
silver  nitrate  gives  good  results.  The  strength  of  the  latter  should  be  about  0.66  </o  and 
the  quantity  about  200  c.c.  to  a  I  c.c.  object.  At  first  a  plentiful  precipitate  is  thrown 
down,  in  which  case  the  solution  should  be  changed,  and  this  probably  repeated  once  more 
after  a  few  hours.  After  twenty-four  hours,  at  the  most  forty-eight  hours,  this  process  is 
usually  completed,  and  the  tissues  may  be  sectioned.  The  sections  must  then  be  care- 
fully dehydrated  with  absolute  alcohol,  cleared  in  creosote  and  mounted  without  a  cover- 
glass  in  Canada  balsam  (the  section  is  mounted  on  a  cover-glass  with  Canada  balsam,  and 
the  cover-slip  then  fastened  over  the  opening  of  a  perforated  slide  with  the  specimen 
downward) . 

In    order  to  obtain  a    uniform  penetration  of    the  objects  by   the  potassium 
bichromate,  the  latter  may  be   first   injected    into  the   vessels.       Golgi  uses    potassium 
bichromate-gelatin  (  2.5  %  of  the  salt,  based  on  the  amount  of  the  softened  gelatin  ;   com- 
pare Golgi,  93).     After  the  injection  and  cooling  of  the  specimen  the  latter  is  cut  in 
4 


50  THE    MICROSCOPIC    PREPARATION. 

small  pieces  and  treated  in  the  manner  previously  described.  Instead  of  Müller' s  fluid, 
that  of  Erlicki  may  be  used,  the  time  of  treatment  being  then  shorter  (from  five  to  eight 
days). 

The  objects  may  also  be  treated  with  a  potassium  bichromate-osmic  acid  solution 
(2.5%  solution  of  potassium  bichromate,  8  vols.;  I%  osmic  acid,  2  vols.),  the  sections 
thus  treated  being  ready  for  immersion  in  silver  nitrate  after  two  or  three  days.  It  is  ad- 
visable to  treat  the  objects  with  the  potassium  bichromate  solution  first,  and  then  with  the 
potassium  bichromate-osmic  mixture.  By  this  method  the  specimens  remain  under  the 
control  of  the  investigator ;  they  may  be  examined  either  at  once,  or  after  an  interval 
varying  between  three  or  four  and  twenty-five  to  thirty  days  after  immersion.  If  then  one 
or  several  pieces  of  tissue  are  taken,  at  intervals  of  two,  three,  or  four  days,  from  the  potas- 
sium bichromate  solution  and  placed  in  the  potassium  bichromate-osmic  acid  mixture, 
and  then  in  the  silver  nitrate  solution,  various  combinations  of  the  fluids  result,  and  the 
investigator  is  usually  rewarded  with  at  least  some  sections  giving  most  excellent 
results. 

Another  one  of  Golgi'  s  methods  consists  in  successive  treatment  with  potassium 
bichromate  and  bichlorid  of  mercury.  After  remaining  in  the  potassium  bichromate  for 
from  three  to  four  weeks  (a  longer  period  is  allowable),  the  objects  are  placed  in  a  0.25  'fo 
Xa  \^o  solution  of  corrosive  sublimate.  In  the  latter  the  specimens  blacken  much  more 
slowly  than  in  the  silver  nitrate  solution — eight  to  ten  days  for  smaller  pieces ;  for  larger 
ones,  two  months,  and  in  some  cases  even  longer.  Before  mounting  the  preparations  in 
glycerin  or  Canada  balsam  they  must  be  carefully  washed  ;  otherwise  pin-shaped  crystals 
form  within  the  sections  and  distort  the  whole  view.  The  metallic  white  of  the  prepara- 
tion may  be  changed  to  black  by  placing  the  celloidin  section  in  a  photographer's  toning 
solution  consisting  of :  (a)  sodium  hyposulphite  175  gm.,  alum  20  gm.,  ammonium  sulpho- 
cyanid  lo  gm.,  sodium  chlorid  40  gm.,  and  water  looo  gm.  (the  mixture  must  stand  for 
eight  days  and  then  be  filtered)  ;  [b)  z.  \fo  gold  chlorid  solution.  The  specimen  is 
placed  for  a  few  minutes  in  a  solution  composed  of  60  c.c.  of  a  and  7  c.c.  of  b,  washed 
again  in  distilled  water,  dehydrated  with  alcohol,  and  mounted  in  Canada  balsam.  After 
toning  and  washing,  the  sections  may  still  be  stained. 

Golgi' s  methods  are  extremely  inconstant  in  their  results.  When  successful,  how- 
ever, only  a  few  elements  are  blackened  each  time,  an  advantage  not  to  be  underesti- 
mated ;  for  if  all  nerves  should  stain  equally  well,  discrimination  between  the  various 
elements  in  the  preparation  would  be  very  difficult.  Neither  are  the  same  structures 
always  impregnated  ;  sometimes  it  is  the  ganglion  cells  and  fibers,  at  other  times  the  neu- 
rogliar  cells,  and  occasionally  only  the  vessels. 

After  the  foregoing  explanation  of  Golgi 's  methods  as  applied  by 
himself,  we  shall  append  a  description  of  these  methods  as  modified  and 
employed  at  the  present  time  (Ramon  y  Cajal,  Kölliker,  von  Lenhossek 
and  others). 

Golgi 's  methods  are  classified  as  the  slow,  the  mixed,  and  the  rapid. 

The  slow  method  requires  a  preliminary  treatment.  Pieces  of  tis- 
sue from  I  to  2  cm.  in  diameter  are  placed  for  from  three  to  five  weeks 
in  a  2  ^  potassium  bichromate  solution  ;  they  are  then  transferred  for  from 
twenty-four  to  forty-eight  hours  to  a  0.75^  silver  nitrate  solution,  or  for 
a  much  longer  time  to  a  0.5^  solution  of  corrosive  sublimate. 

In  the  mixed  method  the  specimens  are  allowed  to  remain  for  four 
or  five  days  in  a  2  ^  aqueous  potassium  bichromate  solution ;  then  for 
from  twenty-four  to  thirty  hours  in  a  mixture  consisting  of  i^  osmic 
acid  I  vol.,  and  2^  potassium  bichromate  solution  4  vols.  They  are 
then  treated  with  a  0.75^  silver  nitrate  solution  for  one  or  two  days- 

When  the  rapid  method  is  employed,  the  specimens  are  immedi- 
ately placed  in  a  mixture  consisting  of  i  vol.  of  1%  osmic  acid  and  4 
vols,  of  a  3.5^  potassium  bichromate  solution,  and,  finally,  for  one  or 
two  days  in  a  0.75^  silver  nitrate  solution,  to  every  200  c.c.  of  which 
one  drop  of  formic  acid  has  been  added. 

When  employing  these  methods,  and  more  particularly  the  one  last 
described  (which  seems  to  be  the  most  efficient),  the  following  conditions 
must  be  carefully  observed  :  If  possible,  the  material  should  be  absolutely 


METHODS    OF    IMPREGNATION.  5 1 

fresh,  the  specimens  must  not  exceed  3  or  4  mm.  in  thickness,  and  for 
every  piece  of  tissue  treated  about  10  c.c.  of  the  osmium-potassium 
bichromate  mixture  should  be  employed,  the  specimens  remaining  in  the 
latter  (in  the  dark)  at  a  temperature  of  25°  C.  for  a  length  of  time  vary- 
ing according  to  the  result  desired  (two  or  three  days  for  the  neurogliar 
cells,  from  three  to  five  days  for  the  ganglion  cells,  and  from  five  to  seven 
days  for  the  nerve-fibers  of  the  spinal  cord).  The  objects  are  now  dried 
with  blotting-paper  or  washed  quickly  in  distilled  water  and  then  placed 
for  two  or  three  days  in  a  o.  75  %  silver  nitrate  solution  at  room-tempera- 
ture. In  this  they  may  remain  for  four  or  five  days  without  damage,  but 
not  longer,  as  otherwise  the  precipitate  becomes  markedly  granular  {vid. 
V.  Lenhossek,  92). 

If  Golgi's  method  be  unsuccessful  (this  applies  to  all  its  modifica- 
tions), the  preparations  may  be  transferred  from  the  silver  nitrate  solu- 
tion back  into  a  potassium  bichromate-osmic  acid  mixture  containing 
less  osmic  acid,  in  which  they  remain  several  days,  and  are  then  again 
placed  in  the  silver  nitrate  solution  for  from  twenty-four  to  forty-eight 
hours.     This  procedure  may  even  be  repeated. 

Cox  obtains  a  precipitate  in  both  cells  and  fibers  by  treating 
small  pieces  of  the  central  nervous  organs  with  a  mixture  composed  of 
potassium  bichromate  20  parts,  5  %  corrosive  sublimate  20  parts,  distilled 
water  30  to  40  parts,  and  5  %  potassium  Chromate  of  strong  alkaline 
reaction  16  parts.  The  specimens  remain  in  this  mixture  from  one  to 
three  months,  according  to  the  temperature,  and  are  then  further  treated 
according  to  Golgi's  method. 

As  the  chrome-silver  preparations  are  not  permanent,  and  can  not, 
therefore,  be  subsequently  stained,  Kallius  has  suggested  that  the  chrome- 
silver  precipitate  be  reduced  to  metallic  silver  by  treatment  with  the 
"quintuple  hydroquinon  developer"  (hydroquinon  5  gm.,  sodium 
sulphite  40  gm.,  potassium  carbonate  75  gm.,  and  distilled  water  250 
gm.).  For  this  purpose  20  c.c.  of  the  solution  are  diluted  with  230  c.c. 
of  distilled  water  ;  this  mixture  may  be  preserved  in  the  dark  for  some 
time  if  desired.  Before  using  this  latter  solution,  it  should  be  mixed  with 
^3,  or  at  the  most  ^,  of  its  volume  of  absolute  alcohol.  The  sections  are 
placed  in  a  watch-crystal  containing  some  of  the  latter  mixture  until  they 
turn  black  (a  few  minutes).  As  soon  as  the  silver  salt  is  completely 
reduced,  the  sections  are  placed  for  from  ten  to  fifteen  minutes  in  70^ 
alcohol,  then  for  five  minutes  in  a  20%  solution  of  sodium  hyposulphite 
and,  finally,  washed  for  some  time  in  distilled  water,  after  which  they 
may  be  stained,  and  even  treated  with  acid  alcohol  and  potassium 
hydrate. 

The  following  simple  method  for  permanently  mounting  Golgi  prepar- 
ations under  a  cover-glass  has  been  recommended  by  Huber. 

After  impregnation  with  chrome-silver  the  tissues  are  hastily  dehy- 
drated, imbedded  in  celloidin,  and  cut  in  sections  varying  from  25  /i  to 
100  IX  in  thickness.  The  sections  are  then  dehydrated  and  placed  for 
from  ten  to  fifteen  minutes  in  creosote,  from  which  they  are  carried 
into  xylol,  where  they  remain  another  ten  minutes.  The  sections  are 
then  removed  to  the  slide.  The  xylol  is  then  removed  by  pressing  sev- 
eral layers  of  filter-paper  over  the  section.  On  removing  the  filter-paper 
the  sections  are  quickly  covered  by  a  large  drop  of  xylol  balsam  and  the 
slide  is  carefully  heated  over  a  flame  for  from  three  to  five  minutes.     Be- 


52  THE    MICROSCOPIC    PREPARATION. 

fore  the  balsam  cools  the  preparation  is  covered  with  a  large  cover-glass, 
warmed  by  passing  several  times  through  the  flame. 

Kopsch  (96)  places  specimens  in  a  solution  composed  of  10  c.c. 
of  formalin  (40^  formaldehyd)  and  40  c.c.  of  a  3.5%  solution  of  potas- 
sium bichromate.  For  objects  2  c.c.  in  size  50  c.c.  of  the  fluid  are  em- 
ployed ;  but  if  the  specimens  be  large,  the  mixture  must  be  changed  in 
twelve  hours.  At  the  end  of  twenty-four  hours  this  fluid  is  replaced  by  a 
fresh  3.5%  potassium  bichromate  solution,  and  the  specimens  are  then 
transferred  to  a  0.75%  solution  of  silver  nitrate  (after  two  days,  if  the 
tissue  be  the  liver  or  stomach ;  and  after  from  three  to  six  days,  if  retina 
or  central  nervous  system).  After  this  treatment  the  objects  are  car- 
ried over  into  40^  alcohol  and,  finally,  into  absolute  alcohol,  imbedded 
as  rapidly  as  possible,  and  cut.  The  sections  are  mounted  in  balsam 
without  a  cover-glass. 

PREPARATION  OF  PERMANENT  SPECIMENS. 

The  resinous  media  used  in  the  final  mounting  of  preparations  are 
Canada  balsam  and  damar. 

Canada  Balsam. — Commercial  Canada  balsam  is  usually  dissolved  in 
turpentine ;  it  should  be  slowly  evaporated  in  a  casserole  and  then  dissolved 
in  xylol,  toluol,  or  chloroform,  etc.  The  proper  concentration  of  the  solu- 
tion is  found  with  a  little  experience.  A  thick  solution  penetrates  the 
interstices  of  the  section  with  difficulty,  and  usually  contains  air-bubbles 
which  often  hide  the  best  areas  of  the  preparation,  and  can  only  be  re- 
moved with  difficulty  by  heating  over  a  flame.  Thin  solutions,  on  the 
other  hand,  have  also  their  disadvantages  ;  they  evaporate  very  quickly,  and 
the  empty  space  thus  created  between  the  cover-slip  and  slide  must  again 
be  filled  with  Canada  balsam.  This  is  best  done  by  dipping  a  glass  rod 
into  the  solution  and  placing  one  drop  at  the  edge  of  the  cover-slip, 
whereupon  the  fluid  spreads  out  between  the  cover-slip  and  slide  as  a 
result  of  capillary  attraction.  Canada  balsam  dries  rather  slowly,  the 
rapidity  of  the  process  depending  upon  the  temperature  of  the  room.  To 
dry  quickly,  the  slides  may  be  held  for  a  few  moments  over  a  gas  or 
alcohol  flame,  or  they  may  be  placed  in  a  warm  oven,  where  the  prepara- 
tions become  so  dry  in  twenty -four  hours  that  they  can  be  examined  with 
an  oil-immersion  lens.  The  oil  used  for  this  purpose  should  be  wiped 
away  from  the  cover-slip  after  examination.  This  can  only  be  done,  with- 
out moving  the  cover-slip,  when  the  balsam  is  thoroughly  dry  and  holds 
the  cover-slip  firmly  in  place. 

Damar. — Damar  is  dissolved  preferably  in  equal  parts  of  oil  of  tur- 
pentine and  benzin.  It  has  the  advantage  of  not  rendering  the  prepara- 
tion as  translucent  as  Canada  balsam.      Otherwise  it  is  used  as  the  latter. 

Clearing  Fluids. — Since  alcohol  does  not  mix  with  Canada  balsam 
or  damar,  an  intermediate  or  clearing  fluid  is  used  in  transferring  objects 
from  the  former  into  the  latter.  Xylol,  toluol,  carbol-xylol  (xylol,  3  parts; 
carbolic  acid,  i  part),  oil  of  bergamot,  oil  of  cloves,  and  oil  of  origanum 
are  ordinarily  used.  The  process  is  somewhat  simpler  where  sections  are 
fixed  to  the  slide.  Xylol  is  dropped  onto  the  surface  of  the  slide,  or  better, 
the  whole  preparation  is  placed  for  a  few  minutes  in  a  vessel  containing 
xylol  until  the  diffusion  currents  have  ceased  (which  may  be  seen  with 
the  naked  eye).  The  slide  is  then  taken  out,  tilted  to  allow  the  xylol  to 
run  off,  wiped  dry  around  the  object  with  a  cloth,  and  placed  upon  the 


METHODS    OF    INJECTION.  53 

table  with  the  specimen  upward.  A  drop  of  Canada  balsam  is  now 
placed  on  the  section  (usually  on  its  left  side),  and  a  clean  cover-slip 
grasped  with  a  small  forceps.  It  is  then  gently  lowered  in  such  a  way 
that  the  Canada  balsam  spreads  out  evenly  and  no  air-bubbles  are  im- 
prisoned under  the  glass.     When  this  is  done  the  preparation  is  finished. 

If  one  is  dealing  with  loose  sections,  a  spatula  or  section-lifter  is 
very  useful  in  transferring  them  from  absolute  alcohol  into  the  clearing 
fluid — carbol-xylol  or  bergamot  oil  (xylol  evaporates  very  rapidly) — and 
from  this  onto  the  slide.  In  doing  this  it  is  necessary  that  the  sec- 
tion should  lie  well  spread  out  on  the  section-lifter,  wrinkles  being  re- 
moved with  a  needle  or  small  camel's-hair  brush.  In  sliding  the  section 
off  the  spatula  (with  a  needle  or  brush)  a  small  quantity  of  the  clearing  fluid 
is  also  brought  onto  the  slide.  This  must  be  removed  as  far  as  possible 
by  tilting  or  with  blotting-paper.  The  section  can  now  be  mounted 
in  Canada  balsam  as  before.  For  esthetic  and  practical  reasons  the 
student  should  see  that  during  the  spreading  of  the  drop  of  Canada  balsam 
the  section  remains  under  the  middle  of  the  cover-slip.  Should  it  float 
to  the  edge,  it  is  best  to  raise  the  cover-slip  and  lower  it  into  place  again. 
The  cover-slip  should  never  be  slid  over  the  specimen. 

Glycerin. — To  mount  in  glycerin  the  sections  are  transferred  from 
water  to  the  slide,  covered  with  a  drop  of  glycerin  and  the  cover -slip  ap- 
plied. This  method  is  employed  in  mounting  sections  colored  with  a 
stain  that  would  be  injured  by  contact  with  alcohol,  and  where  clearing  is 
not  especially  necessary. 

Farrant's  Gum  Glycerin. 

In  place  of  pure  glycerin  the  following  mixture  may  be  used  : 

Glycerin      50  c.c. 

Water      So    " 

Gum-arabic  (powder) 50  gm. 

Arsenious  acid I    " 

Dissolve  the  arsenious  acid  in  water.  Place  the  gum-arabic  in  a  glass  mortar  and 
mix  it  with  the  water;  then  add  the  glycerin.  Filter  through  a  wet  filter-paper  or 
through  fine  muslin. 

To  preserve  such  preparations  for  any  length  of  time  the  cover- 
glasses  must  be  so  fixed  as  to  shut  off  the  glycerin  or  acetate  of  potash 
from  the  air.  For  this  purpose  cements  or  varnishes  are  employed  which 
are  painted  over  the  edges  of  the  cover-slip.  These  masses  adhere  to  the 
glass,  harden,  and  fasten  the  cover-slip  fimily  to  the  slide,  hermetically 
sealing  the  object.  The  best  of  these  is  probably  Krönig' s  varnish,  pre- 
pared as  follows  :  2  parts  of  wax  are  melted  and  7  to  9  parts  of 
colophonium  stirred  in,  and  the  mass  filtered  hot.  Before  employing 
an  oil-immersion  lens  it  is  advisable  to  paint  the  edge  with  an  alcoholic 
solution  of  shellac. 

METHODS  OF  INJECTION. 

The  process  of  injection  consists  in  filling  the  blood-  and  lymph-ves- 
sels with  colored  masses  in  order  to  bring  out  clearly  their  relation  to  the 
neighboring  tissue  elements.  The  instruments  required  are  a  syringe  of 
suitable  size  or  a  constant  pressure  apparatus  and  cannulas  of  various  sizes. 
Serviceable  and  instructive  injections  of  blood-vessels  are  readily  made ; 
good  injections  require  skill,  experience,  and  patience.  Injection  masses 
may  be  classed  under  two  heads — cold  injection  masses  and  warm  injection 


54       ■  THE    MICROSCOPIC    PREPARATION. 

masses.  The  vehicle  of  the  latter  is  most  generally  gelatin.  For  inject- 
ing the  blood-vessels  either  the  cold  or  the  warm  masses  may  be  employed, 
although  the  latter  give  better  results.  The  cold  masses  are  to  be  used 
for  injecting  the  lymphatic  vessels.  In  injecting  the  blood-vessels  it  is 
well  to  wash  out  the  vessels  with  warm  normal  salt  solution  before  the  in- 
jection mass  is  forced  into  the  vessels.  The  following  masses  may  be 
recommended : 

Gelatin=carmin. — The  first  is  a  gelatin -carmin  mass,  and  is 
prepared  as  follows:  (i)  4  gm.  of  carmin  are  stirred  into  8  c.c.  of 
water  and  thoroughly  ground.  Into  this  a  sufficient  quantity  of  ammonia 
is  poured  to  produce  a  dark  cherry  color  and  render  the  whole  transpar- 
ent. (2)  50  gm.  of  finest  quality  gelatin  is  placed  in  distilled  water  for 
twelve  hours  until  well  soaked.  It  is  then  pressed  out  by  hand  and 
melted  at  a  temperature  of  70°  C.  in  a  porcelain  evaporating  dish.  The 
two  solutions  are  now  slowly  mixed,  the  whole  being  constantly  stirred 
juntil  a  complete  and  homogeneous  mixture  is  obtained.  To  this  mass  is 
added,  drop  by  drop,  a  25^  acetic  acid  solution  until  the  color  begins 
to  change  to  a  brick  red  and  the  mass  becomes  slightly  opaque.  This 
should  be  very  carefully  done,  as  a  single  drop  too  much  may  spoil  the 
whole.  During  this  procedure  the  substance  should  be  kept  at  70°  C. 
and  constantly  stirred.  The  change  in  color  indicates  that  the  reaction 
of  the  mass  has  become  neutral  or  even  slightly  acid  (an  ammoniac  solu- 
tion should  not  be  used,  since  the  stain  diffuses  through  the  wall  of  the 
vessel  and  colors  the  surrounding  tissues);  the  whole  is  filtered  through 
flannel  while  still  warm.  As  this  mass  hardens  on  cooling  it  is  injected 
warm.  The  instruments  used  are  also  warmed  before  the  injection  is 
begun. 

Gelatin-Berlin  Blue. — One  part  of  oxalic  acid  is  powdered  in  a 
mortar;  to  this  is  added  one  part  of  Berlin  blue  and  12  parts  of  water. 
Stir  and  rub  until  a  solution  is  obtained.  Prepare  a  gelatin  vehicle  as 
directed  in  the  preceding  paragraph  ;  to  1 2  parts  of  the  gelatin  mass  add 
slowly  while  stirring  12  parts  of  the  Berlin  blue  solution.  The  whole  is 
filtered  through  flannel  while  still  warm. 

Yellov^  Gelatin  Mass  (Hoyer). — Prepare  a  gelatin  vehicle  consist- 
ing of  I  part  of  gelatin  and  4  parts  of  distilled  water;  a  cold,  saturated 
solution  of  bichromate  of  potassium  and  a  cold,  saturated  solution  of  lead 
acetate.  Take  equal  volumes  of  each.  Add  the  bichromate  of  potassium 
solution  to  the  gelatin  and  heat  almost  to  boiling;  then  add  slowly, 
while  stirring,  the  lead  acetate  solution. 

Carmin  Mass,  Cold  (KoUmann). — One  gm.  of  carmin  is  dissolved 
in  a  small  quantity  of  ammonium  hydrate  and  20  c.c.  of  glycerin  added. 
To  another  20  c.c.  of  glycerin  there  is  added  20  drops  of  hydrochloric  acid 
and  this  added  to  the  glycerin -carmin  mixture  while  stirring. 

Saturated  aqueous  solutions  of  Berlin  blue  or  Prussian  blue  may  also  be 
used  for  cold  injections. 

Injection  masses  already  prepared  are  to  be  had  in  commerce. 
Besides  those  already  mentioned,  still  others  colored  with  China  ink,  etc. , 
are  in  general  use. 

Small  animals  are  injected  as  a  whole  by  passing  the  cannula  of 
a  syringe  into  the  left  ventricle  or  aorta.  In  the  case  of  large  animals, 
or  where  very  delicate  injections  are  to  be  made,  the  cannula  is  inserted 
into  one  of  the  vessels  of  the  respective  organs.  The  proper  ligation  of 
the  remaining  vessels  should  not  be  omitted. 


RECONSTRUCTION    BY    MEANS    OF    WAX    PLATES.  55 

Organs  injected  with  carmin  are  fixed  in  alcohol  and  should  not 
be  brought  in  contact  with  acids  or  alkalies.  Such  parts  as  are  injected 
with  Berlin  blue  are  less  sensitive  in  their  after-treatment.  Pieces  or  sec- 
tions that  have  become  pale  regain  their  blue  color  in  oil  of  cloves. 

If  objects  or  sections  injected  with  Berlin  blue  be  treated  with 
a  solution  of  palladium  chlorid,  the  bluish  color  changes  to  a  dark 
brown  which  afterward  remains  unchanged  (Kupffer). 

By  means  of  the  above  injection  methods  other  lumina  can  be 
filled,  as,  for  instance,  those  of  the  glands.  As  a  rule,  these  are  only  par- 
tially filled,  since  they  end  blindly,  and  their  walls  are  less  resistant  and 
may  be  damaged  by  the  pressure  produced  by  the  injection. 

Silver  Nitrate.— In  thin  membranes  and  sections  the  vessel-walls  can 
be  rendered  distinct  by  silver-impregnation,  which  brings  out  the  out- 
lines of  their  endothelial  cells.  This  may  be  done  either  by  injecting  the 
vessel  with  a  i  %  solution  of  silver  nitrate,  or,  according  to  the  process 
of  Chrzonszczewsky,  with  a  0.25%  solution  of  silver  nitrate  m  gelatin. 
This  method  is  of  advantage,  since,  after  hardening,  the  capillaries  ot  the 
.  injected  tissue  appear  slightly  distended.  Organs  thus  treated  can  be 
sectioned,  but  the  endothelial  mosaic  of  the  vessels  does  not  appear  defi- 
nitely until  the  sections  have  been  exposed  to  sunlight. 

The  injecting  of  lymph -channels,  lymph-vessels,  and  lymph- 
spaces  is  usually  done  by  puncture.  A  pointed  cannula  is  thrust  into 
the  tissue  and  the  syringe  emptied  by  a  slight  but  constant  pressure.  The 
injected  fluid  spreads  by  means  of  the  channels  offering  the  least  resist- 
ance For  this  purpose  it  is  best  to  employ  aqueous  solutions  of  Berlin 
blue  or  silver  nitrate,  as  the  thicker  gelatin  solutions  cause  tearing  ot  the 

^^^Tltman's  Process.— To  bring  out  the  blood   capillaries  and  the 
lymphatic  channels,  Altman's  process  (79),  in  which  the  vessels  are  in- 
jected with  olive  oil,  is  useful.     The  objects  are  then  treated  with  osniic 
acid,  sectioned  by  means  of  a  freezing  microtome  and  finally  treated  with 
eau  de   Javelle   (a  concentrated  solution  of  hypochlorite  of  potassium). 
-    By  this  process  all  the  tissues  are  eaten  away,  the  casts  of  the  blood-vessels 
remaining  as  a  dark  framework  (corrosion) .  The  manipulation  of  these  pre- 
parations is  extremely  difficult  on  account  of  the  brittleness  of  the  oil  casts. 
For  lymph-channels  Altman  ii/>id.)  used  the  so-called  oil -impregnation 
Fresh  pieces  of  tissues,  thin  lamellae  of  organs,  cornea,  etc.,  are  placed 
for  five  to  eight  days  in  a  mixture  containing  olive  oil   i  part,  absolute 
alcohol  V^  part,  sulphuric  ether  }4  part  (or  castor  oil  2,  absolute  alcohol 
I     etc  )       The  pieces  are  then  laid  for  several  hours  m  water,  where 
the  externally  adherent  globules  of  oil  are  mechanically  removed  and 
those  in  the  lymph-canalicular  system  are  precipitated.     Ihe  objects  are 
now  treated  with  osmic  acid,   cut  by  means  of  a  freezing  microtome 
and  corroded.     In  this  case,  the  corrosive  fluid  (eau  de  Javelle)  should 
be  diluted  two  or  three  times. 

RECONSTRUCTION  BY  MEANS  OF  WAX  PLATES. 

It  is  often  impossible  to  obtain  a  clear  conception  of  the  form  of  minute 
anatomic  structures,  nor  of  their  relations,  by  means  of  sections  or  by  the 
methods  of  maceration  and  teasing.  To  obviate  such  difficulties  methods  ot 
reconstruction  have  been  devised,  by  means  of  which  such  structures  may 
be  reproduced  in  an  enlarged  form  without  losing  their  inherent  morpho- 


56 


THE    MICROSCOPIC    PREPARATION. 


logic  features.  Of  these  methods,  we  shall  here  describe  that  suggested 
by  Born  (1876)  and  known  as  Bom's  method  of  reconstruction  by  wax 
plates.  This  method  has  found  wide  application  in  embryologic  investi- 
gations, and  has  proved  very  valuable  in  ascertaining  the  form,  relation, 
and  metamorphosis  of  embryonic  structures  and  organs.  It  has  not  been 
so  extensively  used  in  the  study  of  the  form  of  fully  developed  anatomic 
structures  ;  it  deserves,  however,  a  fuller  appreciation  of  its  value  as  an 
aid  in  microscopic  study.  Necessary  are  serial  sections,  wax  plates  of 
desired  thickness,  and  a  drawing  apparatus. 

Serial  Sections. — One  of  the  requisites  of  wax  plate  reconstruction 
is  a  perfect  series  of  sections  of  uniform  thickness.  The  thickness  of 
the  sections  should  depend  on  the  character  and  size  of  the  object  to  be 
reconstructed  and  on  the  magnification  necessary  to  give  the  model  ob- 
tained such  a  size  as  to  enable  it  to  be  readily  manipulated.  In  the 
reconstruction  of  fully  developed  anatomic  structures,  such  as  parts 
of  glands  or  entire  glands,  it  is  generally  not  possible  to  make  an  outline 
drawing  of  the  parts  to  be  reproduced.  When  this  is  possible,  it  forms 
the  first  step  of  the  method. 

Wax  Plates. — Several  methods  have  been  suggested  for  obtaining 
wax  plates  of  uniform  and  desired  thickness.     The  instrument  devised  by 


Fig.  9. — Apparatus  for  making  wax  plates,  used  in  reconstruction  by  Bom's  method. 


Huber  and  figured  in  Fig.  9  may  be  recommended  for  this  purpose.  It 
consists  of  a  heavy  cast-iron  plate,  supported  by  three  adjustable  legs. 
On  two  sides  of  the  plate  are  found  movable  side-pieces  which  may  be 
raised  or  lowered  by  micrometer  screws  to  a  desired  height  and  then 
tightly  clamped.  There  is,  further,  a  heavy  iron  roller  which  runs  on 
the  adjustable  side  pieces.  This  roller  needs  to  be  heated  in  boiling 
water  before  use,  and  is  kept  in  boiling  water  when  not  in  use  during  the 
process  of  making  wax  plates.  The  method  of  making  plates  is  as  fol- 
lows :  The  side  plates  are  adjusted  so  that  their  upper  surface  projects 
above  the  main  plate  for  a  distance  representing  the  thickness  of  the  wax 
plate  desired;  Melted  wax  is  then  poured  on  the  main  plate,  in  an  even 
layer  somewhat  thicker  than  the  wax  plate  desired,  and  then  rolled  out 
with  the  hot  roller  until  the  roller  runs  evenly  on  the  side  pieces.  The 
wax  plate  is  now  allowed  to  cool,  when  it  is  removed  from  the  apparatus 
and  placed  in  a  pan  of  cold  water,  where  it  remains  for  a  few  minutes  or 
until  thoroughly  cooled. 

Drawing  of  the  Portions  of  the  Sections  to  be  Reconstructed. 
— The  drawings  of  the  portions  of  the  sections  representing  the  portion 
to  be  reconstructed,  at  the  magnification  selected,  may  be  made  with  the 


RECONSTRUCTION    BY    MEANS    OF    WAX    PLATES.  5/ 

aid  of  a  camera  lucida,  or  by  means  of  a  projection  apparatus.  Bardeen 
has  devised  a  drawing  table  which  is  placed  horizontally,  over  which  is 
placed  a  mirror  at  an  angle  of  45  degrees.  The  table  may  be  made  to 
move  by  means  of  a  windlass  toward  or  away  from  the  microscope  so 
that  any  magnification  may  be  quickly  obtained.  An  ordinary  micro- 
scope with  the  tube  placed  horizontally  may  be  used,  the  illumination 
being  obtained  from  an  arc  light.  (For  further  details  see  Bardeen, 
"Johns  Hopkins  Bulletin,"  vol.  xii,  p.  148.)  Sharp  outlines  of  the 
parts  to  be  reconstructed  should  be  made  and  the  drawing  for  each  sec- 
tion labelled  with  reference  to  the  series  of  drawings  and  with  reference 
to  the  number  of  the  section,  as  it  is  often  necessary  to  refer  to  the  sec- 
tions while  reconstructing.  After  the  drawings  have  been  completed 
they  are  transferred  to  the  wax  plates,  which  is  conveniently  done  by 
placing  the  drawing  over  the  wax  plate  and  tracing  the  outline  with  a 
blunt-pointed  instrument,  using  some  pressure  while  doing  so.  The  wax 
plates  are  numbered  with  reference  to  the  drawings.  It  is  necessary  to 
maintain  an  equal  ratio  between  the  diameter  of  the  magnification  of  the 
drawing  of  the  sections,  the  thickness  of  the  plates  used  and  the  thickness 
of  the  sections.  Thus,  if  it  is  desired  to  reconstruct  portions  of  a  series 
of  sections  5  /^  in  thickness  and  to  use  wax  plates  2  mm.  thick,  the  draw- 
ings need  to  be  made  at  a  magnification  of  400  diameters. 

Cutting  Out  the  Parts  to  be  Reconstructed  and  Completing 
the  Model. — Those  portions  of  the  wax  plates  representing  the  parts  to 
be  reconstructed  as  outlined  by  the  tracings  are  cut  out  with  a  sharp 
knife  with  narrow  blade,  the  wax  plate  being  placed  on  a  glass  plate 
during  this  procedure.  If  the  parts  of  the  sections  to  be  reconstructed 
consist  of  a  number  of  disjointed  pieces,  these  are  retained  in  their  rela- 
tive positions  by  means  of  remaining  bridges  of  wax,  which  should  be 
firm  enough  to  keep  all  parts  in  their  proper  relation.  The  parts  of  each 
wax  plate  representing  the  portions  of  the  section  to  be  reconstructed  are 
piled  up  in  their  proper  sequence  as  they  are  cut  out.  The  completion  of 
the  model  consists  in  accurately  adjusting  the  portions  obtained  from  each 
wax  plate  to  those  which  precede  and  follow  them.  This  process  is 
facilitated  by  building  up  the  model  in  blocks  representing  five  sections, 
as  has  been  suggested  by  Bardeen.  Those  parts  representing  the  portions 
of  the  sections  to  be  reconstructed  are  united  together  by  pins  or  small 
nails  ;  other  parts,  such  as  wax  bridges,  are  removed  by  means  of  a  hot 
knife.  The  successive  blocks  are  then  similarly  united  and  the  model  is 
completed  by  smoothing  over  the  surfaces  by  means  of  a  hot  iron. 


GENERAL  HISTOLOGY. 
I.  THE  CELL. 

During  the  latter  part  of  the  seventeenth  century,  Hooke,  Mal- 
pighi,  and  Grew,  making  observations  with  the  simple  and  imperfect 
microscopes  of  their  day,  saw  in  plants  small  compartment-like 
spaces,  surrounded  by  a  distinct  wall  and  filled  with  air  or  a  liquid ; 
to  these  the  name  cell  was  applied.  These  earlier  observations  were 
extended  in  various  directions  during  the  latter  part  of  the  seven- 
teenth and  the  eighteenth  century.  Little  advance  was  made, 
however,  until  Robert  Brown  (183 1)  directed  attention  to  a  small 
body  found  in  the  cell,  previously  mentioned  by  F'ontana,  and 
known  as  the  nucleus.  In  the  nucleus  Valentin  observed  (1836) 
a  small  body  known  as  the  nucleolus.  In  1838  Schleiden  brought 
forward  proof  to  show  that  plants  were  made  up  wholly  of  cells, 
and  especially  emphasized  the  importance  of  the  nuclei  of  cells.  In 
1839  Schwann  originated  the  theory  that  the  animal  body  was 
built  up  of  cells  resembling  those  described  for  plants.  Both 
Schleiden  and  Schwann  defined  a  cell  as  a  small  vesicle,  surrounded 
by  a  firm  membrane  inclosing  a  fluid  in  which  floats  a  nucleus. 
This  conception  of  the  structure  of  the  cell  was  destined,  however, 
to  undergo  important  modification.  In  1846  v.  Mohl  recognized  in 
the  cell  a  semifluid,  granular  substance  which  he  named  protoplasm. 
Other  investigators  (Kölliker  and  Bischoff)  observed  animal  cells 
devoid  of  a  distinct  cell  membrane.  Max  Schultze  (1861)  attacked 
vigorously  the  older  conception  of  the  structure  of  cells,  proclaim- 
ing the  identity  of  the  protoplasm  in  all  forms  of  life,  both  plant  and 
animal,  and  the  cell  was  defined  as  a  nucleated  mass  of  protoplasm 
endozved  with  the  attributes  of  life.  In  this  sense  the  term  cell  is 
now  used. 

The  simplest  forms  of  animal  life  are  organisms  consisting  of 
only  one  cell  [frotosoa^.  Even  in  the  development  of  the  higher 
animals,  the  first  stage  of  development,  the  fertilized  &%%,  is  a  single 
cell.  This  by  repeated  division  gives  rise  to  a  mass  of  similar  cells, 
which,  owing  to  their  likeness  in  shape  and  structure,  are  said  to  be 
undifferentiated.  As  development  proceeds,  the  cells  of  this  mass 
arrange  themselves  into  three  layers,  the  germ  layers,  the  outer  one 
of  which  is  the  ectoderm,  the  middle  one  the  mesoderm,  and  the  inner 
one  the  entoderm.  In  the  further  development,  the  cells  of  the 
germ  layers  change  their  form,  assume  new  qualities,  adapting 
themselves  to  perform  certain  definite  functions  ;  a  division  of  labor 
ensues, — the  cells  become  differentiated.    Cells  having  similar  shape 

58 


THE    CELL-BODY. 


59 


and   similar  function  are   grouped  to  form  tissues,  and  tissues  are 
grouped  to  form  organs. 

We  shall  now  consider  the  structure  of  the  cell.      Every  cell 
consists  of  a  cell-body  and  a  nucleus. 


A.  THE  CELL-BODY. 

The  body  of  the  cell  consists  of  a  substance  known  as  proto- 
plasm  or    cytoplasm.      This  is    not    a    substance   having    uniform 


Vacuoles. 


Chromatin  network. 

Linin  network. 
Nuclear  fluid. 

Nuclear  membrane. 


Cell-membrane.   -- 


Exoplasm. ^<r   "' 


Spongioplasm. 
Hyaloplasm. 

Nucleolus. 
Chromatin  net-knot. 

Centrosome. 

Centrosphere. 


Foreign  inclosures.    Metaplasm. 
Fig.  lo. — Diagram  of  a  cell. 

physical  and  chemical  qualities,  but  a  mixture  of  various  organic 
compounds  concerning  which  knowledge  is  not  as  yet  conclusive,- 
but  which  in  general  are  proteid  bodies  or  albumins  in  the  widest 

sense. 

In  spite  of  the  manifold  differences  in  its  composition,  proto- 
plasm exhibits  certain  general  fundamental  properties  which  are 
always  present  wherever  it  is  found.  Ordinarily,  protoplasm  ex- 
hibits certain  structural  characteristics.  In  it  are  observed  two  con- 
stituents,— threads  or  plates,  which  are  straight  or  winding,  which 
branch,  anastomose,  or  interlace,  and  which  are  generally  arranged  in 
a  regular  framework,  network,  or  reticulum.  These  threads  probably 
consist  of  or  contain  small  particles  arranged  in  rows,  called  cell- 
microsomes  {znd.  van  Beneden,  83  ;  M.  Heidenhain,  94;  and  others). 
Benda,  who  has  devoted  much  time  to  the  study  of  certain  proto- 
plasmic structures,  has  found  in  these  threads  small  granules  or 


6o 


THE    CELL. 


rod-shaped  structures  to  which  he  has  given  the  name  "thread- 
granules"  or  mitochondria.  The  mitochondria  can  be  differentially 
stained  and  are  not  distributed  irregularly  through  the  cell  proto- 
plasm, but  in  certain  definite  regions.  They  are  regarded  as  in  part 
identical  with  the  microsomes.  This  thread-like  substance  is  known 
as  protoplasm  in  the  stricter  sense  (Kupffer,  75);  also  as  spongio- 
plasm,  or  the  fibrillar  mass  of  Flemming  (82).  The  other  constit- 
uent of  the  cytoplasm  is  a  more  fluid  substance  lying  between  the 
threads  in  the  meshes  of  the  spongioplastic  network,  and  is  known 
as  paraplasm  (Kupffer),  hyaloplasm,  cytolymph,  or  the  interfibrillar 
substance  of  Flemming.  According  to  most  investigators,  the 
more  important  vital  processes  of  the  cell  are  to  be  identified  with 
the  spongioplasm,  and  are  controlled  by  the  nucleus,  while  the  para- 
plasm assumes  an  inferior  or  passive  role.  With  special  methods 
Altman  (94)  was  able  to  demonstrate  granules  in  the  protoplasm, 
associated  with,  but  not  in  the  spongioplastic  threads.  To  these  he 
gave  the  name  bioblasts,  and  referred  the  vital  qualities  of  the  proto- 
plasm to  them.      Biitschli   believes   the  protoplasm   to   consist   of 


Cilia. 


Fig.  1 1. — Cylindric  ciliated  cells  from  the  primitive  kidney  of  Petromyzon  planeri; 

X  1200. 

separate,  honeycomb-like  spaces,  which  give  it  a  foam-like  structure 
— foam-structure  of  protoplasm. 

Protoplasm  displays  phenomena  of  motion,  shown  on  the  one 
hand  by  contraction,  and  on  the  other  by  the  formation  of  processes 
that  take  the  form  either  of  blunt  projections  or  lobes,  or  of  long, 
pointed,  and  even  branched  threads  or  processes  known  as  pseudo- 
podia.  The  extension  and  withdrawal  of  the  pseudopodia  enable  the 
cell  to  change  its  position.  The  point  of  such  a  process  fastens  to 
some  object  and  the  rest  of  the  cell  is  drawn  forward,  thus  giving  the 
cell  a  creeping  motion — wandering'  cells.  Certain  cells  take  up  and 
surround  foreign  bodies  by  means  of  their  pseudopodia.  If  these 
bodies  are  suitable  for  nutrition,  they  are  assimilated  ;  if  not,  they 
can,  under  certain  circumstances,  be  deposited  by  the  cell  in  cer- 
tain localities  (Metschnikoff's  phagocytes).  Similar  thread-like 
processes  which,  however,  can  not  be  drawn  into  the  cell,  occur  in 
some  cells  in  the  shape  of  cilia,  which  are  in  constant  and  energetic 
motion — ciliated  cells.  Certain  cells  possess  only  a  single  long  pro- 
cess, by  means  of  which  unattached  cells  are  capable  of  direct  or 
rotating  motion — -flagellate  cells,  spermatozoa. 


THE    CELL-BODY.  6l 

Inside  of  the  cell-body  the  protoplasm  also  shows  phenomena  of 
motion,  the  streaming  of  the  protoplasm.  In  plant  cells  there  is 
often  a  noticeable  regularity  in  the  direction  of  the  current.  Men- 
tion should  not  be  omitted  of  the  so-called  molecular  or  Brownian 
movement  in  the  cells,  which  consists  in  a  rapid  whirling  motion 
of  particles  or  granules  suspended  in  the  protoplasm  (Brown). 

Living  protoplasm  is  irritable  in  the  highest  degree,  and  reacts 
very  strongly  to  chemic  and  physical  agents.  It  is  very  sensitive  to 
changes  in  temperature.  All  the  phenomena  of  life  occur  in  greater 
intensity  and  more  rapidly  in  a  warm  than  in  a  cold  temperature, 
this  fact  being  very  strikingly  shown  by  the  phenomena  of  motion 
in  the  cell,  as  also  in  its  propagation.  By  subjecting  protoplasm  to 
different  temperatures,  its  various  movements  can  be  slowed  or 
quickened.      It  dies  in  too  high  or  too  low  a  temperature. 

Certain  substances  coming  in  contact  with  the  cell  from  a  given  direc- 
tion have  on  it  an  attracting  or  repelling  action.  These  phenomena  are 
known  as  positive  and  negative  che?notropis?n  (ychenwtaxis^ .  The  action 
of  chemic  agents  on  the  different  wandering  cells  of  the  body  and  on  cer- 
tain free-swimming  unicellular  organisms  naturally  varies  to  a  great 
degree.  Among  these  phenomena  must  be  included  those  produced  by 
water  (hydrotropism)  and  light  (heliotropism).  It  is  very  probable  that 
all  these  phenomena  are  of  importance  to  the  proper  appreciation  of  some 
of  the  processes  going  on  in  the  vertebrate  body  (as,  for  instance,  in  the 
origin  of  diseases  caused  by  micro-organisms). 

Protoplasm  may  contain  various  structures.  Of  these,  the 
vacuoles  deserve  special  mention.  They  are  more  or  less  sharply 
defined  cavities  filled  with  fluid,  and  vary  considerably  in  number 
and  size.  The  fluids  that  they  contain  differ  somewhat,  but  are 
always  secreted  by  the  protoplasm,  and  are,  as  a  rule,  finally  emp- 
tied out  of  the  cell.  As  a  consequence,  vacuoles  are  best  studied 
where  the  function  of  the  cell  is  a  secretory  one.  Here  they  are 
often  large,  and  sometimes  fill  up  the  whole  cell,  the  contents  of 
which  are  then  emptied  out  (^glandular  cells). 

Contents  of  a  solid  nature,  such  as  fat,  pigment,  glycogen,  and 
crystals,  are  peculiar  to  certain  cells.  By  these  deposits  the 
cell  is  more  or  less  changed,  the  greatest  variation  in  form  taking 
place  in  the  production  of  fat.  The  latter,  as  a  rule,  takes  the  shape 
of  a  globule,  and  greatly  modifies  the  position  of  the  normal  con- 
stituents of  the  cell.  Deposits  of  pigment  alter  the  cells  to  a  less 
degree.  This  substance  occurs  in  the  protoplasm  either  in  solution 
or  in  the  form  of  fine  crystalline  bodies.  Glycogen  is  more  gener- 
ally diffused,  occurring  very  generally  in  embryonal  cells  and  in  the 
liver-  and  cartilage-cells  of  the  adult.  Occasionally  we  find  larger 
crystals  in  animal  cells,  as,  for  instance,  in  the  red  blood-corpuscles 
of  the  teleosts.  So-called  margarin  crystals  sometimes  occur  in 
large  numbers  as  stellate  figures  in  dead  fatty  tissues  kept  at  low 
temperatures. 


62  THE    CELL. 

Many  cells  are  without  a  distinct  cell  membrane,  another  con- 
stituent of  the  protoplasm.  In  such  cells  the  outer  layer  of  the 
protoplasm  is  often  more  homogeneous  and  less  dense  than  that 
lying  more  centrally,  which  has  often  a  more  granular  appearance; 
the  outer  layer  of  the  protoplasm  is  in  such  cells  known  as  the 
exoplasm,  in  contradistinction  to  the  more  granular  endoplasm. 

In  other  cells,  however,  the  outer  layer  of  the  cell-protoplasm 
shows  differentiation,  leading  to  the  formation  of  a  distinct  cell-mem- 
brane (as  in  fat-cells,  cartilage-cells,  goblet-cells,  etc.).  F.  E.  Schulze 
has  given  it  the  name  pellicula  in  cases  where  the  entire  cell  is  sur- 
rounded by  a  homogeneous  layer,  and  cuticula  or  cuticle  where 
only  one  side  of  the  cell  is  supplied  with  the  membrane  (as  in  the 
intestinal  epithelium).  It  is  assumed  that  both  spongioplasm  and 
paraplasm  are  concerned  in  the  formation  of  this  membrane. 

In  the  protoplasm  of  many  cells  there  is  found  a  small  body 
known  as  the  centrosome.  This  is  usually  situated  near  the  nucleus 
of  the  cell,  occasionally  in  the  nucleus.  Generally,  it  has  the  appear- 
ance of  a  minute  granule,  sometimes  scarcely  larger  than  a  micro- 
some. It  is  often  surrounded  by  a  small  area  of  a  granular  or  finely 
reticular  or  radially  striated  cytoplasm,  known  as  the  attraction' 
sphere  or  centrosphere. 

B,  THE  NUCLEUS. 

The  second  constant  element  of  the  cell  is  the  nucleus.  As  a 
rule,  it  is  sharply  defined,  and  in  its  simplest  form  consists  of  a 
round  vesicle  of  a  compHcated  structure  composed  of  several  sub- 
stances. The  form  of  the  nucleus  corresponds  in  general  to  the 
shape  of  the  cell ;  in  an  elongated  cell,  it  is  correspondingly  long, 
and  flattened  where  the  cell  is  plate-like  in  shape.  The  nucleus  of 
a  wandering  cell  that  is  in  the  act  of  passing  through  a  narrow  inter- 
cellular cleft  adapts  itself  to  the  changes  of  form  in  the  cell  without 
being  permanently  altered  in  shape.  In  other  words,  the  nucleus  is 
soft,  and  can  be  easily  distorted  by  any  solid  substances  within  or 
without  the  protoplasm,  only  to  resume  its  original  form  when  the 
pressure  is  removed.  It  possesses,  then,  a  certain  amount  of  elas- 
ticity. Movements  of  certain  nuclei,  entirely  independent  of  the  sur- 
rounding protoplasm,  have  often  been  observed.  It  is  only  rarely 
that  the  general  form  of  the  nucleus  differs  materially  from  the 
general  form  of  the  cell.  This,  however,  occurs  in  the  nuclei  of 
leucocytes  and  many  of  the  giant  cells  of  bone-marrow,  which 
are  often  irregular,  and  may  even  be  ring-shaped.  In  certain  arth- 
rozoa,  branching  forms  of  nuclei  occur,  as  also  in  the  skin  glands 
of  turtles.  The  proportionate  size  of  nucleus  to  cell-body  varies 
greatly  in  different  cells.  Especially  large  nuclei  are  found  in  im- 
mature ova,  in  certain  epithelial  cells,  etc. 

The  contents  of  the  nucleus  consist  of  a  framework  or  reticu- 
lum, in  the  meshes  of  which  there  is  found  a  semifluid  substance. 


THE    NUCLEUS.  63 

In  treating  the  nuclei  with  certain  stains,  the  nuclear  reticulum  will 
be  seen  to  consist  of  two  constituents,  a  substance  appearing  in 
the  form  of  variously  shaped,  minute  granules,  which  stains  deeply, 
and  is,  therefore,  known  as  cliroinatin.  This  is  imbedded  in  and 
deposited  on  a  less  stainable  network,  the  linin.  The  meshes  of  this 
network  are  occupied  by  a  transparent,  semifluid  substance,  which 
does  not  stain  easily,  and  is  known  as  the  achromatic  portion  of  the 
nucleus.  It  is  also  known  as  paralinin,  nuclear  sap,  karyolymph,  or 
nucleoplasm.  Chemically,  chromatin  belongs  to  those  albuminous 
substances  known  as  nucleins. 

In  well-stained  nuclei  of  considerable  size  the  chromatin  gran- 
ules are  seen  closely  placed  in  a  continuous  row  throughout  the  net- 
work of  linin,  which  penetrates  the  nuclei  in  all  directions.  In 
every  resting  nucleus  one  or  more  small  round  bodies  are  found 
imbedded  in  the  nucleoplasm.  These  are  known  as  true  7tucleoli, 
and  do  not  stain  quite  so  deeply  as  the  chromatin.  The  fact  that 
certain  reagents  dissolve  the  chromatin,  but  not  the  true  nucleoli, 
proves  that  the  substance  of  which  the  latter  are  composed  is  not 
identical  with  chromatin, — and  is,  therefore,  known  as  paramiclein 
(F.  Schwartz). 

In  many  cases  we  find  in  the  linin,  granules  of  a  substance 
known  as  lanthanin,  which  displays  a  marked  affinity  for  the  so- 
called  acid  anilin  stains,  in  contradistinction  to  chromatin,  which 
stains  principally  with  .the  basic  anilin  colors.  These  are  known  as 
oxychromatin  granules  in  contradistinction  to  the  basichromatin 
granules  of  the  chromatin  (M.  Heidenhain,  94). 

The  true  nucleoli  should  not  be  confused  with  the  slight  swell- 
ings of  the  chromatin  network  found  at  the  junction  of  the  threads, 
and  known  as  net-knots,  or  karyosomes. 

Surrounding  the  resting  nucleus  is  usually  a  nuclear  nievibrane 
(amphipyrenin)  resembling  in  many  respects  chromatin.  As  a  rule, 
it  does  not  form  a  continuous  layer,  but  is  perforated,  having  open- 
ings that  contain  nuclear  fluid.  We  have,  then,  both  substances, 
chromatin  and  nucleoplasm,  as  elements  of  the  nuclear  membrane. 
Besides  this,  the  nuclear  membrane  receives  an  outer  layer,  differ- 
entiated from  the  protoplasm.  Later  investigations  have  shown 
that  even  during  a  period  of  rest  the  relationship  of  the  nucleus  to 
the  protoplasm  of  the  cell  is  much  more  intimate  than  was  hereto- 
fore believed  {vid.  Reinke,  94). 

A  resting  nucleus — i.e.,  one  not  in  process  of  division — usually 
consists,  therefore,  of  a  sharply  defined  membrane  (amphipyrenin), 
which  has  in  its  interior  a  chromatic  (nuclein)  and  an  achromatic 
(linin)  network,  a  nuclear  fluid  (paralinin),  and  nucleoli  (paranuclein). 

The  chromatin  of  the  nucleus  is  not  always  in  the  form  of  a  net- 
work. In  some  cases — as,  for  instance,  in  the  premature  ova  of 
certain  animals  (O.  Hertwig,  93.  II)  and  in  spermatozoa — it  is  col- 
lected in  compact  bodies.  In  the  ova  it  may  often  be  mistaken  for 
a  true  nucleolus  (germinal  spot).  In  this  case,  however,  it  consists 
of  nuclein,  and  not  of  paranuclein. 


64  THE    CELL. 

C.  NUCLEAR  AND  CELL-DIVISION, 

The  founders  of  the  cell  theory  believed  in  what  may  be  known 
as  a  modification  of  the  theory  of  spontaneous  generation,  stating  that 
cells  might  originate  from  a  structureless  substance  known  as  kyto- 
blastema  or  blastema,  in  which  a  nucleus  was  formed  by  precipita- 
tion. Henle  (1841)  drew  attention  to  the  fact  that  cells  might  mul- 
tiply by  the  separation  of  small  portions  of  the  cell-body,  a  process 
known  as  budding ;  and  Barry  (1841)  stated  that  during  the  multi- 
plication of  cells  the  nuclei  divided.  The  same  year  Remak 
observed  division  of  cells  in  the  blood  of  embryos.  Goodsir  (1845) 
originated  the  theory  that  all  cells  were  developed  from  preexisting 
cells.  This  was  first  clearly  stated  as  a  general  law  by  Virchow 
(1855),  and  his  saying,  "  Oninis  cellida  e  cellula,"  is  constantly  being 
verified.  Our  more  accurate  knowledge  of  cell-division  dates,  how- 
ever, from  more  recent  times  (1873-80),  when  Schneider,  Fol,  Stras- 
burger, Flemming,  and  many  others  demonstrated  that  during  the 
division  of  the  cell  the  nucleus  passed  through  a  series  of  compli- 
cated changes  which  resulted  in  an  exact  division  of  the  chromatin. 

The  phenomena  which  usher  in  cell-division  are  especially 
noticeable  in  the  nucleus,  the  elements  of  which  are  arranged  and 
transformed  in  a  typic  manner.  During  the  division  of  the  nucleus 
the  nuclear  membrane  is  lost,  and  the  relationship  of  the  substances 
of  the  nucleus  to  the  protoplasm  of  the  cell  is  a  very  intimate  one. 
As  a  consequence,  during  the  middle  phases  of  division  there  is  no 
well-defined  demarcation  between  the  nucleus  and  the  cell-body. 
As  a  rule,  the  mother  cell  and  nucleus  divide  into  two  daughter 
cells,  each  having  a  nucleus,  alike  in  every  particular.  It  was  early 
observed,  however,  that  occasionally  cells  divided  by  a  much  sim- 
pler process,  in  which  case  the  nucleus  did  not  pass  through  such 
complicated  changes.  Accordingly,  two  distinct  types  of  cell- 
division  are  recognized,  which  are  distinguished  as  mitosis,  karyoki- 
nesis,  or  indirect  cell-division,  and  aniitosis,  or  direct  cell-division. 
Both  lead  to  the  formation  of  two  nuclei,  which  are  known  as 
daughter  nuclei  as  distinguished  from  the  original  mother  nucleus. 

J.  MITOSIS  OR  KARYOKINESIS  (INDIRECT  CELL-DIVISION). 

The  description  of  the  process  of  mitotic  cell-division  is  compli- 
cated by  the  fact  that  structural  changes  are  observed  which  occur 
simultaneously  in  the  nucleus,  centrosome,  and  cytoplasm.  This 
fact  should  be  borne  in  mind,  as,  for  the  sake  of  clearness,  a  sepa- 
rate description  of  the  changes  involving  each  of  these  structures 
seems  demanded.  The  process  of  mitotic  cell-division  may  be 
divided  into  four  periods  or  phases,  which  follow  one  another  with- 
out clearly  defined  limits  : 

The  prophases,  in  which  the  nuclear  membrane  disappears,  the 
chromatin  is  transformed  into  definite  threads,  and  the  centrosome 


NUCLEAR    AND    CELL-DIVISION. 


65 


r-SP 


Figs.  12-21. — Ten  stages  of  mitotic  nuclear  division  from  the  oral  epithelium  of  the 
larva  of  a  salamander.  (Plate  I,  Sobotta  and  Ruber's  "Atlas  and  Epitome  of  Human 
Histology,"  1903)  :  Fig.  12,  Cell  with  resting  nucleus  ;  Fig.  13,  cell  with  nucleus  at  the 
beginning  of  mitosis;  Fig.  14,  nuclear  membrane  has  disappeared,  chromosomes  in  a 
loose  skein,  pole  field  at  the  left;  Fig.  15,  monaster- viewed  from  above  ;  Fig.  16,  mo- 
naster viewed  from  the  side,  achromatic  spindle  is  also  shown  ;  Fig.  17,  monaster  viewed 
from  the  side,  with  chromosomes  crowded  closely  about  the  equator  of  the  spindle  ;  Fig. 
18,  stage  of  metakinesis  ;  Fig.  19,  diaster  with  beginning  constriction  of  the  cell-body: 
Fig.  20,  dispirem  with  completion  of  the  cell  division;  Fig.  21,  telophase. 


and  centrosphere  undergo  important  changes.     This  is  the  prepar- 
atory stage. 

The  nietaphases,  in  which  the  division  and  the  separation  of  the 
chromatin  take  place. 

The  anaphases,  in  which  the  daughter  nuclei  are  formed  and  the 
cell-protoplasm  begins  to  divide. 

The  telophases,  in  which  the  division  of  the  cell  is  completed. 
5 


66 


THE    CELL. 


Fig.  25.  Fig.  26. 

Figs.  22-26. — Mitotic  cell-division  of  fertilized  whitefish  eggs — Coregonus  albus. 
Fig.  22,  Cell  with  resting  nucleus,  centrosome,  and  centrosphere  to  the  right  of  the 
nucleus  ;   Fig.    23,  cell  with   two   centrospheres,  with    polar  rays  at  opposite  poles   of 
nucleus;   Fig.  24,  spirem ;  Fig.  25,  monaster;   Fig.  26,  metakinesis  stage. 


To  give  a  better  understanding  of  the  process  we  have  inserted 
a  series  of  figures  in  which  several  phases  of  mitotic  division  are 
portrayed.  In  figures  12—21  are  shown  ten  stages  of  mitotic  nu- 
clear division  from  the  oral  epithelium  of  the  larva  of  a  salamander, 
in  which  changes  undergone  by  the  nucleus  and  centrosome  are 
clearly  brought  out.  And,  further,  a  series  of  figures  (22—29)  show- 
ing the  different  phases  of  mitotic  cell-division  of  the  fertilized  eggs 
of  the  whitefish  (^Coregonus  albus) ;  the  changes  involving  the  centro- 
some, centrosphere,  and  cytoplasm  are  illustrated.  Figure  30,  show- 
ing a  small  portion  of  a  section  through  the  testis  of  the  salamander, 
the  object  in  which  Flemming  first  observed  this  compHcated  series 
of  changes,  presents  the  appearance  more  generally  seen  during 
mitotic  cell-division  of  the  tissue  cells  of  the  higher  vertebrates. 

{a)  Prophases. — The  changes  occurring  in  the  nucleus  will 
be  considered  first.  At  the  beginning  of  the  process  of  mitosis,  the 
chromatin  network,  consisting  of  chromatin  granules,  is  transformed 
into  a  twisted  skein  of  threads,  beginning  at  the  periphery  of  the 


NUCLEAR    AND    CELL-DIVISION. 


67 


Fig.  27. 


Fig.  28. 


Fig.  29. 

Figs  27-29. — Mitotic  cell-division  of  fertilized  whitefish  eggs — Coregomis  albus. 
Fig.    27,   Metakinesis  stage;   Fig.  28,  diaster;   Fig.  29,  late  stage  of  dispirem,   the 
cell -protoplasm  almost  divided. 


nucleus.  This  skein  of  threads  is  known  as  the  spirem  or  mother 
skein,  and  may  appear  as  a  single  thread,  which  breaks  up  into  a 
definite  number  of  segments,  or  the  segments  may  appear  as  such 
when  the  skein  is  forming.  At  first  the  threads  are  coarse  and  often 
somewhat  irregular,  staining  much  more  deeply  than  the  linin 
network.  The  separate  segments  of  chromatin  are  known  as 
chromosomes  (Waldeyer,  88).  They  appear,  as  a  rule,  in  the  form 
of  rods  varying  in  length  and  thickness,  and  staining  very  deeply, 
and  often  bent  into  characteristic  U-shaped  loops.  The  bent  portion 
of  each  loop  is  called  its  crown.  "  Every  species  of  plant  or  ani- 
mal has  a  fixed  and  characteristic  number  of  chromosomes,  which 
regularly  recurs  in  the  division  of  all  its  cells  ;  and  in  all  forms 
arising  by  sexual  reproduction  the  number  is  even"  (Wilson,  96). 
In  man  the  number  of  chromosomes  is  given  as  sixteen  by  Barde- 
leben  (92)  and  Wilson  (96),  and  as  twenty-four  by  Flemming  (98). 
During  the  formation  of  the  spirem  the  nuclear  membrane,  as  a 
rule,  disappears.  The  nucleolus  is  also  lost  sight  of,  although  the 
manner  of  its  disappearance  can  not  be  definitely  stated.  The  net- 
knots  are  no  doubt  taken  up  by  the  chromosomes.      The  chromo- 


68  THE    CELL. 

somes  are  now  free  in  the  protoplasm  ;  gradually  the  crown  of  each 
chromosome  approaches  the  center  of  the  space  occupied  by  the 
nucleus,  and  the  chromosomes  form  a  characteristic,  radially 
arranged  stellate  figure,  known  as  the  monaster,  in  the  equatorial 
plane  of  the  cell.  During  the  progress  of  the  changes  affecting  the 
chromatin  of  the  nucleus  and  resulting  in  the  formation  of  the 
chromosomes,  important  phenomena  are  observed,  connected  partly 
with  the  achromatic  substance  of  the  nucleus,  more  especially  with 
the  centrosome,  centrosphere,  and  cytoplasm  of  the  cell.  These 
phenomena  result  in  the  formation  of  a  complicated  structure  known 
as  the  achromatic  spindle  or  amphiaster.  Its  development  is  as  fol- 
lows :  The  centrosome  and  centrosphere,  as  has  been  stated,  usu- 
ally lie  in  the  protoplasm  to  one  side  of  the  nucleus.  If,  at  the  be- 
ginning of  the  division,  the  centrosome  be  single,  it  divides,  and  the 
two  centrosomes  begin  to  separate,  causing  a  division  of  the  centro- 
sphere. Between  the  centrosomes  are  usually  seen  finely  drawn-out 
connecting  threads.  The  centrosomes,  each  of  which  is  surrounded 
by  a  centrosphere,  now  move  apart,  and  a  structure  known  as  the 
central  spindle,  and  consisting  of  fine  threads  arranged  in  the  form 
of  a  spindle,  develops  between  them.  At  each  end  of  the  central 
spindle  is  found  a  centrosome  surrounded  by  a  centrosphere  from 
which  radiate  into  the  cytoplasm  fine  fibers  known  as  polar  rays. 
During  the  formation  of  the  achromatic  spindle  the  nuclear  mem- 
brane disappears  and  the  chromosomes  develop,  as  above  described. 
Some  fibers,  which  seem  to  have  their  origin  from  the  centrosphere, 
grow  into  the  spirem  formed  of  chromosomes,  which  they  appear  to 
pull  into  the  equatorial  plane  of  the  cell,  which  is  also  the  equator 
of  the  central  spindle.  Thus,  the  nuclear  figure  above  described 
as  the  monaster  is  formed.  In  other  cases  the  centrosomes 
and  centrospheres  continue  moving  apart  until  opposite  each  other 
and  separated  by  the  nucleus  (Figs.  23,  24).  As  the  nuclear 
membrane  disappears  and  the  spirems  and  chromosomes  are  form- 
ing, the  central  spindle  develops,  its  fibers  running  from  centro- 
sphere to  centrosphere.  The  polar  rays  also  develop  in  the  cyto- 
plasm at  the  same  time.  As  the  central  spindle  develops,  the 
chromosomes  arrange  themselves  or  are  arranged  about  its  equator 
— monaster. 

{U)  Metaphases. — Usually,  during  the  formation  of  the  monaster, 
or  immediately  after  its  formation  (sometimes  in  the  spirem  stage  or 
even  earlier),  the  most  important  process  of  cell-division  takes 
place.  Each  chromosome  divides  longitudinally  into  two  daughter 
chromosomes.  The  loops  first  divide  at  the  crown,  the  cleft  extend- 
ing up  either  limb  until  the  free  ends  are  reached.  The  smallest 
particle  of  chromatin  divides,  retaining  the  exact  relative  position  in 
the  twin  chromosomes  that  it  possessed  in  the  mother  chromo- 
some. The  daughter  chromosomes  now  wander  over  the  central 
spindle,  their  crowns  presenting,  in  opposite  directions  toward  the 
poles  of  the  cell.     This  process  is  known  as  metakinesis.    Two  stel- 


NUCLEAR    AND   CELL-DIVISION. 


69 


late  figures  are  developed  about  the  respective  poles  of  the  central 
spindle.  The  appearance  presented  is  known  as  a  diaster.  Our 
knowledge  of  the  part  taken  by  the  amphiaster  or  achromatic 
spindle  in  metakinesis  is  not  above  controversy.  It  would  appear, 
however,  that  certain  cytoplastic  fibers,  which  arise  from  the  cen- 
trosphere  and  hang  over  the  central  spindle  and  chromosomes, 
designated  as  mantle  fibers,  assist  in  drawing  the  daughter  chromo- 
somes toward  the  poles  of  the  central  spindle. 

ic)  Anaphases. — After  the  formation  of  the  diaster,  the  loops  be- 
longing to  each  stellate  figure  are  joined  together  to  form  a  skein, 
thus  forming  the  dispircni.  The  chromatin  threads  of  the  two 
skeins  gradually  assume  the  disposition  found  in  the  resting  nucleus. 
This   process   takes  place  in   such  a  way  that  the  threads  of  the 


Dispirem. 


Diaster. 


Diaster. 


Monaster. 


Resting  nucleus. 
Metakinesis. 

Diaster. 
Daughter  cells. 


Spirem. 
Fig.  30. — Mitotic  division  of  cells  in  testis  of  salamander  (Benda  and  Guenther). 


skeins  (or  the  single  thread)  send  out  lateral  processes.  These 
interlace,  and  little  by  little  reproduce  the  network  of  the  resting 
nucleus  ;  at  the  same  time  the  nuclear  membrane  and  the  nucleolus 
reappear.  In  this  stage  the  changes  that  lead  to  the  division  of  the 
cell-body  are  observed.  In  some  cases  the  division  of  the  cell-body 
is  ushered  in  by  an  equatorial  differentiation  of  the  connecting 
threads  of  the  central  spindle.  Chains  of  granules,  arranged  in 
double  rows,  are  seen  to  appear  in  this  region.  The  cell  now  begins 
to  contract  at  its  equator,  the  contraction  extending  between  the 
two  chains  of  granules  until  the  cell  is  completely  di\'ided.  At 
this  time,  also,  the  threads  of  the  amphiaster  disappear  or  are  drawn 
into  the  nucleus.  The  centrosomes,  with  centrospheres,  again  lie 
by  the  side  of  the  daughter  nuclei. 


70  THE    CELL. 

According  to  the  opinion  of  C.  Rabl  (85),  there  remains  in  the 
nucleus,  even  after  it  has  fully  returned  to  a  state  of  rest,  a  polar 
arrangement  of  the  chromatin  loops — that  is,  an  arrangement  of  the 
axis  of  the  loops  in  the  direction  of  the  centrosphere.  The  area 
toward  which  the  crowns  of  the  loops  point  is  known  as  the  polar 
field. 

The  equatorial  differentiation  of  the  connecting  threads  of  the 
central  spindle,  above  mentioned,  was  first  observed  in  vegetable 
tissue,  and  is  known  as  the  cell-plate.  (Fig.  29.)  In  animal  cells  such 
a  plate  is  relatively  rare,  and,  when  seen,  is  found  developed  in  a 
rudimentary  form  (v.  Kostanecki  92,  I). 

{d^  Telophases  (M.  Heidenhain  94). — In  these  phases  of  mitosis 
the  cell  divides  completely.  The  daughter  nuclei  and  centrospheres, 
which  do  not  yet  occupy  their  normal  position  in  the  daughter  cells, 
show  movements  that  result  in  their  assuming  their  normal  positions. 

From  our  description  it  is  seen  that  the  anaphases  represent  the 
same  stages  as  the  prophases,  only  in  an  inverted  sequence.  In  the 
latter  case,  the  result  is  the  resting  nucleus,  while  the  prophases  lead 
to  the  metaphases. 

The  fertilized  ovum  also  divides  by  indirect  nuclear  division. 
(Figs.  22—29.)  From  it  are  derived,  by  this  process,  the  seg- 
mentation cells,  or  blastonieres,  from  which  the  whole  embryo  is 
developed. 

{/)  The  Heterotypic  Form  of  Mitosis. — The  above-described 
type  of  indirect  or  mitotic  nuclear  division  {Jionieotypic  mitosis)  is 
the  usual  one.  Variations,  however,  occur,  as,  for  instance,  in  the 
so-called  heterotypic  form  of  division  (Flemming  87),  which  occurs 
in  certain  cells  of  the  testes  (spermatocytes).  In  this  form  the  first 
stages  are  lacking,  the  nucleus  possessing  from  the  beginning  a 
skein-like  structure.  The  longitudinal  splitting  and  division  of  the 
chromatin  threads  take  place  during  the  first  spirem  stage,  after  which 
there  is  a  phase  in  which  the  figure  may  be  compared  with  an  aster 
of  ordinary  mitosis,  although  the  free  ends  of  the  threads  in  this 
case  are  seldom  observed.  The  latter  is  due  to  the  fact  that  after 
the  longitudinal  splitting,  the  ends  of  the  chromosomes  remain 
united,  or,  if  entire  separation  occurs,  they  are  again  joined.  In  this 
way  closed  loops  are  formed  extending  from  pole  to  pole.  Later 
the  threads  break  at  the  equator  and  move  toward  the  poles,  again 
dividing  to  form  the  daughter  stars. 

2.  AMITOSIS. 

Very  different  from  the  indirect  form  of  nuclear  division  is  the 
direct  or  amitotic.  It  appears  to  occur  seldom  as  a  normal  process, 
and  is  only  exceptionally  followed  by  a  subsequent  cell-division 
{vid.  Flemming,  91,  III).  As  a  consequence,  this  process,  in  most 
cases,  results  in  the  formation  of  polynuclear  cells  (polynuclear  leu- 
cocytes,  giant-cells,  etc.).        The   complicated    nuclear   figures    of 


PROCESS    OF   FERTILIZATION.  7' 

indirect  division  are  here  entirely  absent.  The  nucleus  merely  con- 
tracts at  a  certain  point  and  separates  into  two  or  more  fragments 
(direct  fragmentation,  Arnold)  ;  often  the  nucleus  first  assumes  an 
annular  form  and  then  breaks  up  into  several  fragments,  which 
remain  loosely  connected  (polynuclear  cells).  Centrospheres  are 
also  present,  and  appear  to  take  a  prominent  part  in  the  whole  pro- 
cess, although  the  exact  relationship  between  the  achromatni  and 
chromatin  has  not  as  yet  been  determined. 

Nemiloff  has  recently  called  attention  to  two  locations  where 
amitotic  divisions  may  readily  be  observed— namely,  in  the  large 
surface  cells  of  transitional  epithelium  of  the  bladder  of  mammals 
and  in  the  lymphoid  tissue  layer  of  the  liver  of  amphibia.  In  the 
cells  of  the  former  type  the  nuclear  division  is  initiated  by  a  division 
of  the  nucleolus  which  is  followed  by  a  division  of  nucleus  and  later 
the  protoplasm.  Centrosomes  and  attraction  spheres  were  not 
noticed  in  these  cells.  The  division  of  the  lymphoid  cells  of  the 
amphibian  Hver  is  initiated  by  a  depression  found  in  one  side  of 
their  spherical  nuclei.  This  depression  deepens  until  the  nuclei  be- 
come perforated  and  assume  an  annular  shape.  These  ring-shaped 
nuclei  then  break  through  in  two  or  more  places  and  two  or  more 
daughter  nuclei  are  formed.  During  the  process  of  division  a  cen- 
trosome  with  attraction  sphere  may  often  be  observed,  generally 
situated  in  the  depression  which  initiates  the  division  and  later  in 
the  center  of  the  perforated  nucleus.  Its  role  in  the  division  of  the 
nucleus  and  the  cell-body  is,  however,  not  fully  understood. 

D*  PROCESS  OF  FERTILIZATION. 

The  sexual  cells  form  a  special  group  among  cells  in  general 
Before  the  division  of  the  egg-cell  leading  to  the  development  of 
the  embryo  can  take  place,  the  ovum  must  be  impregnated  (the  so- 
called  parthenogenetic  ova  are  an  exception  to  this  rule).     Fertili- 
zation is  produced  by  the  male  sexual  cell,  the  spermatozoon. 

The  process  of  fertiUzation  consists  in  a  conjugation  of  two  sex- 
ual cells,  and  in  this  process  certain  peculiarities  in  the  behavior  of 
both  cells  must  be  mentioned. 

The  cell  forming  the  ovum  and  the  one  forming  the  spermato- 
zoon must  pass  through  certain  stages  before  fertilization  can  be 
accomplished.  These  consist  in  the  loss  of  half  their  chromosomes 
by  the  nuclei  of  both  sexual  cells.  In  this  way  are  produced  the 
matured  sexual  cells  (ova  and  spermatozoa),  which  retain  on  y 
half  of  the  number  of  chromosomes  of  a  somatic  (body-)  cell. 
In  the  conjugation  of  the  male  and  female  sexual  cells  their  nuclei 
unite  to  form  a  single  nucleus,  known  as  the  segmentation  nucleus. 
Consequently,  this  nucleus  contains  the  same  number  of  chromo- 
somes as  does  that  of  a  somatic  cell. 

In  its  earlier  developmental  stages  the  ovum  is  an  indifferent  cell, 
the  nucleus  of  which   is   known  as  the  germinal  vesicle.     As  the 


72 


THE    CELL. 


Membrane  of 
ovum. 

Nucleus  of . 

ovum. 
Spermatozoon 

entering. 

Protoplasm  of 
ovum  with 
deutoplastic 
granules. 


Fig.  31. 


Female 
pronu- 
cleus. 


Head    of 
spermato- 
zoon with 
centro- 
some. 


Female 
pronu- 
cleus. 


Male 
pronu- 
cleus. 


Fig.  32.  Fig.  33. 

Figs.   31-33. — Diagrams  of  the  process  of  fertilization,  after  Boveri. 
Figure  31,  the  ovum  is  surrounded  by  spermatozoa,  one  of  which  is  in   the  act  of 
penetration.      Toward  it  the  yolk  is  pushed  forward  in  a  short,  rounded  process.      Figure 
32,  the  tail  of  the  spermatozoon  has  disappeared.      Beside  the  head  is  a  centrosome  with 
polar  radiation.     Figure  33,  the  pronuclei  approach  each  other. 

ovum  matures  the  germinal  vesicle  approaches  the  periphery,  and  a 
peculiar  metamorphosis,  which  may  be  regarded  as  a  double,  un- 
equal division  of  the  egg-cell,  takes  place.  One  portion,  in  the  case 
of  both  divisions,  is  much  smaller  than  the  other,  and  is  known  as 
a  polar  body.  At  the  close  of  these  divisions,  during  which  the 
chromosomes  have  been  reduced  to  half  the  original  number,  there 
are,  therefore,  two  polar  bodies  and  the  matured  ovum,  which  is 
now  ready  for  impregnation. 

The  development  of  the  male  sexual  cell  in  its  earlier  stages  is  sim- 
ilar to  that  of  the  ovum.  They  are  derived  from  cells  known  as  sper- 
matogones. These  divide  into  equal  parts,  forming  the  cells  of  a 
second  generation,  the  spermatocytes.  From  a  further  division  of  the 
spermatocytes,  during  which  division  the  chromosomes  are  reduced 
to  half  the  number,  the  spermatids  are  produced.  These  latter  are 
then  changed  directly  into  spermatozoa.  The  reduction  division  of 
the  egg-cell  and  that  of  the  spermatocytes  is  in  principle  the  same, 
except  that  in  spermatogenesis  all  cells  become  matured  sexual  cells 


PROCESS    OF   FERTILIZATION. 


73 


—  Centrosome. 


Female  pro- 
nucleus. 


Chromo- 
somes of 
egg-nu- 
cleus. 


Chromo- 
somes of 
male  pro- 
nucleus. 

Centrosome. 


Fig.  34- 


Fig.  35- 


Chromosomes 
from  egg-nu- 
cleus. 


Chromosomes 
from   sperm- 
nucleus  (male 
pronucleus). 


Centrosome. 


Fig.  36. 

Figs.   34-36. — Diagrams  of  the  process  of  fertilization,  after  Boveri. 
Figure  34,  from  the  spirems  in  the  pronuclei,  chromosomes  have  been  formed.     The 
cenirosphere  has  divided.      Figure  35,  the  double  chromosomes  of  the  two  pronuclei  lie  in 
the  equatorial  plane  of  the  ovum.      Figure  36,  the   ovum   has   divided.      Chromosomes 
from  the  male  and  female  elements  are  seen  in  equal  numbers  in  both  daughter  nuclei. 


(spermatozoa).  In  short,  there  is  here  an  absence  of  structures 
analogous  to  the  polar  bodies,  which  degenerate  after  maturation 
of  the  ovum. 

The  spermatozoa  are  flagellate  cells.  The  head  consists  prin- 
cipally of  nuclear  substance,  to  which  is  added  a  smaller  middle- 
piece  containing,  according  to  the  investigations  of  Fick,  the  centro- 
some. These  two  portions  of  the  male  sexual  cell,  the  head-  and 
middle-piece,  are  the  most  important,  and  are  exclusively  con- 
cerned in  fertilization,  the  flagellum  or  tail  playing  no  part  in  this 
process. 

The  spermatozoon  usually  penetrates  the  ovum  after  the  iirst 
polar  body  has  been  extruded.  The  tail  disappears  during  this 
process,  being  either  left  at  the  periphery  of  the  egg  or  dissolved  in 
the  protoplasm.  From  this  time  the  head  represents  the  so-called 
jna/e  proimclc2is,  and  the  middle-piece  the  centrosome.  From  this 
stage  the  male  pronucleus  undergoes  changes,  the  first  of  which 
consists  of  a  loosening;  of  the  chromatin.      Chromatin  granules  are 


74  THE    CELL, 

formed,  which  later  arrange  themselves  in  the  form  of  chromo- 
somes. 

After  the  second  polar  body  has  been  extruded,  the  chro- 
matin remaining  in  the  ovum  is  transformed  into  the  female  pro- 
nucleus. The  latter  then  approaches  the  male  pronucleus,  the 
membranes  of  both  nuclei  disappearing.  The  chromosomes  of 
the  two  nuclei  thus  formed  are  of  equal  number,  and  now  come  to 
lie  together.  After  a  longitudinal  division  of  the  chromosomes, 
the  daughter  chromosomes  glide  along  the  filaments  of  the  achro- 
matic spindle,  developed  from  the  centrosome  of  the  male  pronu- 
cleus, toward  its  two  poles,  as  in  ordinary  mitosis.  This  they  do 
in  such  a  manner  that  an  equal  distribution  of  the  male  and  female 
daughter  chromosomes  results.  Then,  follow  the  stages  of  the  ana- 
phase. 

From  the  above  description  of  the  process  of  fertilization  it  is 
seen  that  it  consists,  in  the  end,  of  a  union  of  the  nuclei  of  both 
sexual  cells. 

If  paternal  qualities  are  inherited  by  the  offspring,  this  can  only 
take  place  through  the  nucleus,  or  through  the  centrosome  of  the 
male  sexual  cell.  In  other  words,  it  can  be  safely  said  that  these 
structures,  or  the  nucleus  alone,  are  the  principal  means  of  trans- 
mitting inherited  qualities.  The  same  may  also  be  said  of  the 
female  pronucleus.  There  is  no  doubt  that  the  first  two  seg- 
mentation cells  of  the  ovum  are  equally  provided  with  male  and 
female  nuclear  elements.  Since  all  future  cells  are  derivatives  of 
these  two,  it  is  possible  that  the  nucleus  of  every  somatic  cell 
(body-cell)  is  hermaphroditic. 


E.  CHROMATOLYSIS. 

In  the  living  organism  many  cells  are  destroyed  during  the 
various  physiologic  processes  and  replaced  by  new  ones.  On  the 
death  of  a  cell,  changes  take  place  in  its  nucleus  which  result  in  its 
gradual  disappearance.  These  processes,  which  seem  to  follow 
certain  definite  but  as  yet  unfamiliar  laws,  have  been  known  since 
their  study  by  Flemming  (85,  I)  by  the  name  of  chromatolysis 
(karyolysis).  The  nuclei  during  the  course  of  these  changes  show 
many  varied  pictures. 

TECHNIC. 

In  a  fresh  condition,  cells  do  not  show  much  of  their  internal 
structure.  Epithelial  cells  of  the  oral  cavity,  which  can  easily  be  ob- 
tained and  examined  in  the  saliva,  show  really  nothing  except  the  cell 
outlines  and  the  nuclei.  More,  however,  can  be  seen  in  young  ova  iso- 
lated from  the  Graafian  follicles  of  mammalia  ;  or  the  examination  may  be 
facilitated  by  using  the  ovary  of  a  young  frog.  Tissues  that  are  especially 
adapted  for  the  observation  of  cells  in  a  fresh  condition  are  small  ova, 
blood-corpuscles,  and  epithelia  of  certain  invertebrate  animals  (shellfish, 


CHROMATOLYSIS.  75 

etc.).      Unicellular  organisms  such  as  amebae,  infusoria,  and  many  low 
forms  of  vegetable  life  make  also  good  material  for  this  purpose. 

Protoplasmic  currents  are  best  seen  in  the  tactile  hairs  of  the  net- 
tle. Should  fresh  animal  cells  be  desired,  amebae  can  occasionally  be 
found  in  muddy  or  marshy  water.  The  same  phenomena  may  be  ob- 
served in  the  leucocytes  of  the  frog  or,  better  still,  in  the  blood  of  the 
crab. 

In  order  to  make  a  detailed  study  of  the  minute  relationship 
of  the  different  cellular  structures,  it  is  necessary  to  fix  the  cells  ;  the 
same  is  true  of  nuclear  division  and  cell  proliferation.  Although  this 
process  has  been  observed  in  living  cells,  it  was  not  until  it  had  been 
thoroughly  worked  out  in  preserved  preparations.  The  best  results  in  the 
study  of  the  cell  are  obtained  by  methods  that  will  be  subsequently 
described.      Fresh  tissues  are  absolutely  essential. 

According  to  Hammer,  mitosis  in  man  does  not  cease  immediately 
after  death.  The  nuclei  suffer  chromatolytic  destruction,  and  the  achro- 
matic spindle  is  the  last  element  to  disappear. 

Flemming's  solution  here  deserves  first  mention  as  a  fixative.  The 
tissues  ai;e  imbedded,  sectioned,  and  stained  with  safranin.  An  equally 
good  fixative  is  Hermann's  solution,  which  may  be  combined  with  a  sub- 
sequent treatment  witti  pyroligneous  acid.  Rabl  fixes  with  a  o.  i-o.  12  ^^ 
solution  of  Chlorid  of  platinum,  washes  with  water,  passes  into  gradually 
stronger  alcohols,  then  stains  with  Delafield's  hematoxylin,  and  finally 
examines  the  preparation  in  methyl  alcohol. 

Mitoses  can  also  be  seen  by  fixing  in  corrosive  sublimate, 
picric  acid,  chromic  acid,  etc.,  and  staining  in  bulk  with  hematoxylin 
or  carmin,  although  perhaps  not  so  well  as  by  the  preceding  method. 
The  objects  to  be  examined  are  best  when  obtained  from  young  and  grow- 
ing animals,  especially  those  possessing  large  cells.  Above  all  are  to  be 
recommended  the  larvae  of  amphibia,  like  the  frog,  triton,  and  sala- 
mander. If  examination  by  means  of  sections  be  undesirable,  thin 
structures  should  be  procured,  such  as  the  mesentery,  alveoli  of  the  lungs, 
epithelium  of  the  pharynx,  urinary  bladder,  etc.  These  have  the  advan- 
tage of  enabling  one  to  observe  the  whole  cell  instead  of  parts  or  frag- 
ments of  cellular  structures.  In  sections  of  a  larva  that  has  been  fixed  in 
toto,  mitotic  figures  can  be  seen  in  almost  all  the  organs,  and  are  particu- 
larly numerous  in  the  epithelium  of  the  epidermis,  gills,  central  canal  of 
the  brain  and  spinal  cord,  etc.  Other  organs,  such  as  the  blood,  liver, 
and  muscle,  also  show  mitoses. 

Certain  vegetable  cells  are  peculiarly  adapted  to  the  study  of 
mitosis,  as,  for  instance,  those  in  the  ends  of  young  roots  of  the  onion. 
The  onion  should  be  placed  in  a  hyacinth  glass  filled  with  water  and  kept 
in  a  warm  place.  After  two  or  three  days  numbers  of  small  roots  will 
be  found  to  have  developed.  Beginning  at  the  points,  pieces  5  milli- 
meters in  length  are  cut,  which  are  treated  in  the  same  manner  as  animal 
tissues.  These  are  then  cut,  either  transversely  or  longitudinally,  into 
very  thin  sections  (not  over  5  ^t  in  thickness).  In  one  plane,  polar  views 
of  the  mitoses  are  obtained  ;   in  the  other,  lateral  views. 

The  methods  used  for  demonstrating  the  remaining  parts  of  the 
cell  and  its  nucleus  (except  the  chromatin)  are,  as  a  rule,  more  compli- 
cated, and  consequently  less  reliable.  In  order  to  see  the  centrosome, 
the  spindle   fibrils,   the  linin  threads,  and   the  polar  rays,   one   of  the 


76  THE    CELL. 

methods  already  described  may  be  used;  viz.,  the  treatment  with  pyro- 
ligneous  acid  of  objects  previously  fixed  in  osmic  acid  mixtures. 

According  to  Hermann  (93,  II),  sections  from  such  preparations 
can  be  doubIe=stained  as  well  as  those  that  have  not  been  treated  with 
pyroligneous  acid.  They  are  accordingly  stained  with  safranin  in  the 
usual  manner,  and  afterward  treated  from  three  to  five  minutes  with 
the  following  solution  of  gentian  violet :  5  c.c.  of  a  saturated  alco- 
holic solution  of  the  stain  is  dissolved  in  100  c.c.  of  anilin  water. 
The  latter  is  composed  of  4  c.c.  of  anilin  oil  in  100  c.c.  of  distilled 
water.  This  is  shaken  in  a  test-tube  and  then  filtered  through  a  wet 
filter.  The  sections  are  then  placed  in  a  solution  of  iodin  and  iodid  of 
potassium  (iodin  i  gm.,  iodid  of  potassium  2  gm.,  water  300  c.c.) 
until  they  have  become  entirely  black,  after  which  they  are  immersed  in 
alcohol  until  they  receive  a  violet  tinge  with  a  slight  dash  of  brown.  By 
this  means  the  chromatin  network,  the  resting  nuclei,  and  the  chromosomes 
in  both  of  the  spirem  stages  appear  bluish-violet,  while  the  true  nucleoli 
are  pink.     The  chromosomes  of  the  aster  and  diaster  are  colored  red. 

Flemming  (91,  III)  recommends  the  following  method:  Fixation  by 
his  mixture;  the  specimens  or  thin  sections  are  then  placed  in  safranin 
from  two  to  six  days,  washed  for  a  short  time  in  distilled  water,  and  then 
immersed  in  absolute  alcohol  weakly  acidulated  \lith  hydrochloric  acid 
(i  :  1000),  until  no  more  color  is  given  off.  They  are  then  washed  again 
with  distilled  water  and  placed  in  a  concentrated  solution  of  anilin-water- 
gentian-violet  from  one  to  three  hours.  After  a  third  rinsing  in  distilled 
water,  they  come  into  a  concentrated  aqueous  solution  of  orange  G,  until 
they  begin  to  assume  a  violet  color.  Then  wash  with  absolute  alcohol, 
clear  in  clove  or  bergamot  oil,  and  mount  in  Canada  balsam. 

A  comparatively  simple  method  showing  the  different  structures 
of  the  cell  and  its  nucleus  with  great  clearness  consists  in  staining  with 
Heidenhain' s  hematoxylin. 

Solger  (89,  I  and  91)  has  discovered  that  both  chromosomes 
and  polar  rays  are  shown  in  an  exquisite  manner  in  the  pigment  cells  of 
the  skin  (corium)  of  the  frontal  and  ethmoidal  regions  of  the  common 
pike  {vid.  Fig.  37).  The  preliminary  treatment  is  optional,  Flemming's 
solution  or  corrosive  sublimate  being  the  best.  These  cells  illustrate  the 
stability  of  the  radiate  structures  of  protoplasm,  the  polar  rays  showing 
as  parallel  rows  of  pigment  granules. 

The  various  structures  of  resting  and  dividing  nuclei  and  cells 
are  of  such  a  complicated  nature  that  they  can  be  observed  only  with 
great  difficulty  in  ordinary  objects,  because  of  the  crowding  of  so  many 
elements  into  a  comparatively  small  space.  For  example,  salamandra 
maculosa,  which  has  become  a  classic  histologic  object  through  the 
researches  of  Flemming,  possesses  somatic  cells  whose  nuclei  have  no  less 
than  twenty-four  chromosomes.  (It  may  here  be  remarked  that,  curiously 
enough,  salamandra  atra  has  only  half  this  number. )  Consequently,  van 
Beneden's  discovery  (83),  that  the  somatic  cells  of  ascaris  megalocephala 
have  only  four  primary  chromosomes,  is  a  fact  of  considerable  import- 
ance. Boveri  (87,  II  and  88)  has  even  found  an  ascaris  showing  only 
two  chromosomes.  As  these  animals  also  show  distinct  achromatic  fig- 
ures in  the  protoplasm  of  their  ova  and  sperm  cells,  they  are  certainly 
worthy  of  being  regarded  as  typic  specimens  for  laboratory  purposes. 
The  processes  of  cell-proliferation  are  almost  diagrammatic  in  their  dis- 
tinctness. 


CHROMATOLYSIS.  T7 

After  opening  the  abdominal  wall  of  the  animal,  the  ovisacs  are 
removed,  their  numerous  convolutions  separated  as  much  as  possible, 
and  then  fixed  for  twenty-four  hours  in  a  picric-acetic  acid  solution 
(a  concentrated  aqueous  solution  of  picric  acid  diluted  with  2  vols, 
of  water  to  which  i  per  cent,  glacial  acetic  acid  is  added).  Then  fol- 
lows washing  for  twenty-four  hours  with  water,  after  which  the  specimen 
is  transferred  to  increasing  strengths  of  alcohol  (Boveri,  ibid.).  Differ- 
ent regions  of  the  ovisacs  contain  ova  in  various  stages  of  development, 
those  nearest  the  head  containing  cells  ripe  and  ready  for  fecundation, 
while  in  the  more  posterior  regions  are  ova  in  varying  stages  of  segmen- 
tation showing  mitoses.  Specimens  fixed  in  the  manner  above  described 
can  be  stained  with  a  borax-carmin  solution.  After  staining,  the  ova  are 
gently  pressed  out  with  needles  upon  a  slide,  separated,  covered  with  a 
cover- glass,  and  cleared  by  gradual  irrigation  with  glycerin.  The  ova, 
especially  the  segmentation  spheres,  are  very  small,  and  can  be  examined 
only  under  high  magnification.  In  spite  of  the  minuteness  of  the  ob- 
ject and  the  fact  that  the  yolk  does  not  take  the  stain,  and,  on  account  of 


Fig.  37. — Pigment  cell  from  the  skin  of  the  head  of  a  pike  ;   X  650. 

its  high  refractive  index,  distorts  the  picture  to  a  considerable  extent,  the 
mitotic  figures  are  beautifully  distinct. 

Certain  methods  of  treatment  bring  out  in  both  cells  and  nuclei 
the  presence  of  peculiar  granules.  The  latter  have  been  especially 
studied  and  described  by  v.  Altmann  (94,  2d  ed.).  The  methods  that 
he  applies  are  as  follows  :  The  specimens  of  organs  of  recently  killed 
animals  are  fixed  in  a  mixture  consisting  of  equal  volumes  of  a  5'yi^ 
aqueous  solution  of  potassium  bichromate  and  a  2^  solution  of  osmic 
acid,  remaining  in  the  mixture  for  twenty-four  hours.  They  are  then 
washed  for  several  hours  in  water  and  treated  with  ascending  strengths 
of  alcohol ;  viz.,  70,  90,  and  100%.  The  specimens  are  now  placed  in 
a  solution  of  3  parts  of  xylol  and   i   part  of  absolute  alcohol,  then  in 


78  THE    CELL. 

pure  xylol,  and  finally  in  paraffin.      The  tissues  imbedded  in  paraffin 
must  not  be  cut  thicker  than  i  to  2  ;«. 

Altmann  mounts  according  to  the  following  method  :  A  rather  thick 
solution  of  caoutchouc  in  chloroform  (the  so-called  traumaticin  of  the 
Pharmacopeia — i  vol.  guttapercha  dissolved  in  6  vols,  chloroform)  is 
diluted  before  use  with  25  vols,  of  chloroform  and  the  resulting  mixture 
poured  upon  a  slide.  The  latter  is  tilted,  and  after  evaporation  of  the 
chloroform,  heated  over  a  gas  flame.  The  paraffin  sections  are  mounted 
upon  the  slides  so  prepared  and  then  painted  with  a  solution  of  guncotton 
in  aceton  and  alcohol  (2  gm.  guncotton  dissolved  in  50  c.c.  of  aceton, 
5  c.c.  of  which  is  diluted  with  20  c.c.  of  absolute  alcohol).  After  painting 
with  this  solution,  the  sections  are  firmly  pressed  upon  the  slide  with 
tissue  paper,  and  after  drying  are  made  to  adhere  more  closely  by  slight 
warming.  Fixation  to  the  slide  with  water  is  equally  good.  The  sections 
can  now  be  treated  with  various  staining  solutions  without  becoming 
detached  from  the  slides.  The  paraffin  is  gotten  rid  of  by  immersing  in 
xylol,  after  which  the  specimens  are  placed  in  absolute  alcohol.  Fuchsin  S. 
can  be  used  as  a  stain  (20  gm.  fuchsin  S.  dissolved  in  100  c.c.  anilin 
water).  A  small  quantity  of  this  solution  is  placed  upon  the  section, 
and  the  slide  warmed  over  a  flame  until  its  lower  surface  becomes  quite 
perceptibly  warm  and  the  staining  solution  begins  to  evaporate.  The 
slide  is  then  allowed  to  cool,  washed  with  picric  acid  (concentrated 
alcoholic  solution  of  picric  acid  diluted  with  2  vols,  of  water),  after 
which  it  is  covered  with  a  fresh  quantity  of  picric  acid,  and  again,  but 
this  time  vigorously,  heated  (one-half  to  one  minute).  Occasionally 
the  same  results  can  be  obtained  by  covering  the  section  for  five  minutes 
with  a  cold  solution  of  picric  acid  of  the  above  strength.  This  last 
procedure  has  a  decided  influence  upon  the  granula,  and  gives  rise  to  a 
distinct  differentiation  between  them  and  the  remaining  portions  of  the 
cell,  the  latter  appearing  grayish-yellow,  while  the  granula  themselves 
appear  bright  red.  In  some  cases  where  the  granula  can  not  be  sharply 
differentiated  from  the  remaining  structures,  it  may  be  necessary  to 
repeat  the  staining  process.  Xylol-Canada  balsam  should  not  be  used 
for  mounting,  as  it  has  a  bleaching  effect  upon  the  osmic  acid  in  the 
specimen.  Mount  either  in  liquid  paraffin  (Altmann)  or  in  undiluted 
Canada  balsam,  which  is  easily  reduced  to  a  fluid  state,  whenever  needed, 
by  heating. 

There  is  another  method  used  by  Altmann  which  deserves  mention, 
but  practical  application  of  which  must  be  improved  upon  in  the  future ; 
this  consists  in  freezing  the  specimens  and  drying  them  for  a  few  days  in 
the  frozen  condition  in  a  vacuum  over  sulphuric  acid  at  a  temperature  of 
about  — 30°  C. 

According  to  Fischer,  dilute  solutions  of  pepton  when  treated  with 
various  reagents  (especially  with  a  potassium  bichromate-osmium  mix- 
ture) form  precipitates  and  granules  which  are  remarkable  in  that  they 
react  to  stains  exactly  as  do  Altmann's  granula.  It  is,  therefore,  doubt- 
ful whether  Altmann's  granules  should  be  regarded  as  vital  structures. 

Altmann  (92)  has  also  devised  a  simpler  negative  method  for 
demonstrating  the  granula.  Fresh  specimens  are  placed  for  twenty-four 
hours  in  a  solution  consisting  of  molybdate  of  ammonium  2.5  gm., 
chromic  acid  0.35  gm.,  and  water  100  c.c.  ;  then  treated  for  several 
days  with  absolute  alcohol,  sectioned  in  paraffin,  and  colored  with  a 
nuclear  stain  such  as  hematoxylin  or  gentian.     The  intergranular  network 


THE    TISSUES.  79 

is  colored,  vv^hile  the  granula  remain  colorless.  The  amount  of  chromic 
acid  used  (0.25  to  1%)  varies  according  to  the  object  treated  ;  if  molyb- 
date  of  ammonium  alone  be  used,  the  nuclei  will  appear  homogeneous, 
while  if  an  excess  of  chromic  acid  be  employed,  the  nuclei  will  appear 
coarsely  reticulated.  This  method  leads  to  the  formation  of  granula  in 
the  cells  as  well  as  in  the  nucleus. 

Biitschli's  Foam=structure. — Fixing  is  done  either  in  picric  acid 
solution  or  in  weakly  iodized  alcohol.  The  specimens  are  then  stained 
with  iron-hematoxylin — /.  e.,  first  treated  with  acetate  of  iron,  rinsed  in 
water,  and  transferred  to  a  0.5%  aqueous  solution  of  hematoxylin  (simi- 
lar to  the  method  of  R.  Heidenhain).  Very  thin  sections  are  required 
(^  to  I  ,a).  Mounting  is  done,  when  the  lighting  is  good,  in  media 
having  low  refractive  indices,  which  emphasize  the  alveolar  or  foam -like 
structure  of  the  protoplasm.  Of  various  animal  objects,  Bütschli  espe- 
cially recommends  young  ovarian  eggs  of  teleosts,  and  blood-cells  and 
intestinal  epithelium  of  the  frog,  etc.  It  is  still  a  matter  of  uncertainty 
whether  or  not  the  structures  are  actually  present  in  living  protoplasm. 


II.  THE  TISSUES. 

The  first  few  generations  of  cells  which  result  from  the  segmen- 
tation  of  the  fertilized  ovum  have  no  pronounced  characteristics. 
They  are  embryonic  cells  of  rounded  form,  and  are  known  as  blas- 
tomeres.  As  they  increase  in  number  they  become  smaller  and  of 
polygonal  shape,  owing  to  the  pressure  to  which  they  are  subjected. 
From  the  mass  of  blastomeres,  known  as  the  morula  mass,  there 
are  formed,  under  various  processes  described  under  the  name  of 
gastrulation,  two  layers  of  cells,  the  so-called  primary  genn  layers, 
of  which  the  outer  is  the  ectoderm,  the  inner  the  entoderm.  To  the 
primary  germ  layers  is  added  still  a  third  layer,  called  the  meso- 
derm; it  is  derived  from  both  the  ectoderm  and  entoderm,  but 
principally  from  the  latter.  From  these  three  layers  of  cells,  known 
as  the  primary  blastodermic  layers,  are  developed  all  the  tissues,  each 
layer  developing  into  certain  tissues  that  are  distinct  for  this  layer. 
In  their  further  development  and  differentiation  the  cells  of  the  blas- 
todermic layers  undergo  a  change  in  shape  and  structure  character- 
istic for  each  tissue,  and  there  is  developed  an  intercellidar  substance 
varying  greatly  in  amount  and  character  in  the  several  tissues.  In 
the  tissues  developed  from  the  ectoderm  and  entoderm  the  cellular 
elements  give  character  to  the  tissue,  while  the  intercellular  sub- 
stance is  present  in  small  quantity;  in  the  majority  of  the  tissues 
developed  from  the  mesoderm,  the  intercellular  substance  is  abun- 
dant, while  the  cellular  elements  form  a  less  conspicuous  portion. 

The  tissues  derived  from  the  ectoderm  are  : 

The  epidermis  of  the  skin,  with  the  epidermal  appendages  and 
glands  ;  the  epithelium  hning  the  mouth,  with  the  salivary^  glands 
and  the  enamel  of  the  teeth  ;  the  epithelium  and  glands  of  the  nasal 
tract  and  the  cavities  opening  into  it ;  the  lens  of  the  eye  and  retina, 


80  THE    TISSUES. 

and  the  epithelium  of  the  membranous  labyrinth  of  the  ear  ;  and 
finally,  the  entire  nervous  system,  central  and  peripheral. 

From  the  entoderm : 

The  epithelium  lining  the  digestive  tract,  and  all  glands  in  con- 
nection with  it,  including  the  liver  and  pancreas  ;  the  epithelium  of 
the  respiratory  tract  and  its  glands  ;  the  epithelium  of  the  bladder 
and  urethra  (in  the  male,  only  the  prostatic  portion,  the  remainder 
being  of  ectodermal  origin). 

The  cells  of  the  mesoderm  are  early  differentiated  into  three 
groups  (Minot,  99)  : 

(a)  Mesotheliuni. — The  mesothelial  cells  retain  the  character  of 
epithelial  cells.  They  form  the  lining  of  the  pleural,  pericardial, 
and  peritoneal  cavities,  and  give  origin  to  the  epithelium  of  the  uro- 
genital organs  (with  the  exception  of  the  bladder  and  urethra),  and 
striated  and  heart  muscle  tissue. 

(b)  Mesenchyme,  from  which  are  derived  all  the  fibrous  connective 
tissues,  cartilage,  and  bone,  involuntary  muscle  tissue,  the  spleen, 
lymph-glands,  and  bone-marrow  ;  and  cells  of  an  epithelioid  charac- 
ter, lining  the  blood  and  lymph-vessels  and  lymph-spaces,  known 
as  endothelial  cells. 

(c)  Mesavieboid  cells,  comprising  all  red  and  white  blood-cells. 

It  would  be  extremely  difficult  to  attempt  a  classification  of  tis- 
sues according  to  their  histogenesis,  as  identical  tissue  elements  owe 
their  origin  to  different  germinal  layers.  The  classification  adopted 
by  us  is  based  rather  on  the  structure  of  the  tissues  in  their  adult 
stage. 

We  distinguish  : 

A.  Epithelial  tissues  with  their  derivatives. 

B.  Connective  tissues  ;  adipose  tissue  ;  supporting  tissues  (car- 
tilage, bone). 

C.  Muscular  tissue. 

D.  Nervous  tissue. 

E.  Blood  and  lymph. 


A»  EPITHELIAL  TISSUES. 

Epithelial  tissues  are  nonvascular,  and  composed  almost  wholly 
of  epithelial  cells,  united  into  continuous  membranes  by  a  substance 
known  as  intercellular  cement.  They  serve  to  protect  exposed 
surfaces,  and  perform  the  functions  of  absorption,  secretion,  and 
excretion. 

The  epithelia  are  developed  from  all  of  the  three  layers  of  the 
blastoderm. 

They  secrete  the  cement-substance  found  between  their  contigu- 
ous surfaces.  This  takes  the  form  of  thin  lamellae  between  the  cells, 
gluing  them  firmly  together.  In  certain  regions  the  epithelial  cells 
develop  short  lateral  processes  (prickles),  which  meet  like  structures 


EPITHELIAL    TISSUES.  öl 

from  neighboring  cells,  thus  forming  intercellular  bridges.  Between 
these  bridges  are  intercellular  spaces  filled  Avith  lymph-plasma  for 
the  nourishment  of  the  cells.  Epithelia  do  not,  as  a  rule,  possess 
processes  of  any  length.  However,  it  would  appear  that  the  base- 
ment membranes,  situated  beneath  the  epithelia,  consist  chiefly  of 
processes  from  the  basal  portion  of  the  cells.  Some  authors  ascribe 
to  them  a  connective-tissue  origin,  a  theory  which  conflicts  with  the 
fact  that  such  membranes  are  present  in  the  embryo  before 
connective  tissue,  as  such,  has  been  developed  {inembrana  prima, 
Hensen,  'j6). 

The  free  surfaces  of  epithelia  often  support  cuticidar  structures 
which  are  to  be  regarded  as  the  products  of  the  cells.  The  cutic- 
ulse  of  neighboring  cells  fuse  to  form  a  cuticidar  membrane  or  mar- 
ginal zone  which  can  be  detached  in  pieces  of  considerable  size 
(cuticula).  In  longitudinal  sections  the  cuticula  show,  in  many 
cases,  a  striation  which  would  seem  to  indicate  that  they  are  com- 
posed of  a  large  number  of  rod-like  processes  cemented  together  by 
a  substance  possessing  a  different  refractive  index.  The  cell-body  is 
also  striated  for  more  than  half  its  length,  corresponding  to  the  rods 
of  the  marginal  zone.  In  the  region  of  the  nucleus  at  the  basal  por- 
tion the  striation  disappears,  the  cell  here  consisting  of  granular  pro- 
toplasm of  a  more  indifferent  character. 

Since  one  surface  of  each  epithelial  layer  lies  free,  and  is  conse- 
quently exposed  to  other  conditions  than  the  inner  surface,  certain 
differences  are  noticed  between  the  two  ends  of  each  cell.  The 
cells  may  develop  cuticular  structures  as  above  stated.  In  other 
cases  motile  processes  (cilia)  are  developed  on  their  exposed  surface, 
which  move  in  a  definite  direction  in  the  medium  surrounding: 
them,  and  by  means  of  this  motion  sweep  away  foreign  bodies.  It 
is  not  strange  that  the  free  surface  of  the  epithelia,  exposed  as  it  is 
to  stimulation  from  without,  should  develop  special  structures  for 
the  reception  of  sensations  (sense  cells). 

On  the  other  hand,  the  inner  or  basal  surfaces  of  the  cells  usually 
retain  a  more  indifferent  character,  and  serve  for  the  attachment  of 
the  cells  and  the  conveyance  of  their  nourishment.  For  this  reason 
the  nuclei  of  such  cells  are  usually  situated  near  the  basal  surface. 

From  the  above  it  is  seen  that  the  two  ends  of  the  epithelial  cell 
undergo  varying  processes  of  differentiation,  the  outer  being  adapted 
more  to  the  animal,  the  inner  more  to  the  vegetative  functions. 
This  differentiation  has  recently  been  known  as  the  polarity  of  the 
cell.  This  polarity  appears  to  be  retained  even  when  the  cell  loses 
its  epithelial  character  and  assumes  other  functions  (Rabl,  90). 

With  {q.^^  exceptions,  blood-  and  lymph-vessels  do  not  penetrate 
into  the  epithelia,  but  the  latter  are  richly  supplied  with  nerves. 
The  finer  morphology  of  the  epithelia  will  be  described  in  the  chap- 
ters on  the  different  organs  in  Part  II. 

Epithelia  are  classified  according  to  the  shape  and  relation  of 
the  epithelial  cells. 


82 


THE    TISSUES. 


We  give  the  following  classification  : 

1.  Simple  epithelia  (with  or  without  cilia). 

(a)  Squamous  epithelium. 
(&)   Cubic  epithelium. 

(c)  Columnar  epithelium. 

(d)  Pseudostratified  columnar  epithelium. 

2.  Stratified  epithelia  (with  or  without  cilia). 

(a)  Stratified  squamous  epithelium,  with  superficial 

flattened  cells  (without  cilia). 
(^)   Transitional- epithelium, 
(r)   Stratified   columnar   epithelium,  with  superficial 

columnar  cells  (with  or  without  cilia).    . 

3.  Glandular  epithelium. 

4.  Neuro-epithelium. 


J.  SIMPLE  EPITHELIUM. 

In  simple  epithelia  the  cells  lie  in  a  single  continuous  layer. 
Simple  epithelia  are  very  widel)^  distributed.      They  line  almost 
the  entire  alimentary  tract,  the  smaller  respiratory  passages  and  air 


Fig.  38. — Isolated  cells  of  squamous  epithe- 
lium (surface  cells  of  the  stratilied  squamous 
epithelium  lining  the  mouth):  a,  a,  Cells  present- 
ing under  surface  ;  d,  cell  with  two  nuclei. 


Fig-     39- — Surface    view    of 
squamous  epithelium  from  skin  of  a 

frog;  X  400. 


sacs,  the  majority  of  the  gland  ducts,  the  oviducts  and  uterus,  and  the 
central  canal  of  the  spinal  cord  and  ventricles  of  the  brain. 

(a)  Simple  Squamous  Epithelium. — In  simple  squamous  epi- 
thelium the  cells  are  flattened.  Their  contiguous  surfaces  appear 
regular,  forming,  when  seen  from  above,  a  mosaic.  The  nuclei  lie, 
as  a  rule,  in  the  middle  of  the  cell,  and  if  the  latter  be  very  much 
flattened,  the  position  of  the  nucleus  is  made  prominent  by  a  bulg- 
ing of  the  cell  at  this  point.      It  occurs  in  the  alveoli  of  the  lung. 

(6)  Simple  Cubic  Epithelium. — Epithelial  cells  of  this  type 
differ  from  the  above  only  in  that  they  are  somewhat  higher.  They 
appear  as  short  polygonal  prisms.  Their  outlines  are,  as  a  rule,  not 
irregular,  but  form  straight  lines.      Cubic  epithelium  occurs  in  the 


EPITHELIAL    TISSUES. 


83 


smaller  and  smallest  bronchioles  of  the  lungs,  in  certain  portions  of 
the  uriniferous  tubules  and  their  collecting  ducts,  in  the  smaller 
ducts  of  salivary  and  mucous  glands,  liver,  pancreas,  etc. 

(c)  Simple  Columnar  Epithelium. — In  this  type  the  cells  take 
the  form  of  prisms  or  pyramids  of  varying  length.  Cuticular 
structures  are  especially  well  developed.  Columnar  epithelium 
occurs  in  the  entire  intestinal  tract  from  the  cardiac  end  of  the 
stomach  to  the  anus,  in  certain  portions  of  the  kidney,  etc. 


Goblet  cell. 
Cuticular  border. 


Fig.  40. — Simple  columnar  epithelium  from  the  small  intestine  of  man  :  a,  Isolated  cells  ; 
b,  surface  view  ;  c,  longitudinal  section. 


Simple  ciliated  columnar  epithelium  is  found  in  the  oviduct  and 
uterus,  central  canal  of  the  spinal  cord,  and  smaller  bronchi. 

{d)  Pseudostratified  Columnar  Epithelium. — This  type  is 
one  in  which  all  the  cells  rest  on  a  basement  membrane,  but  they 
are  so  placed  that  the  nuclei  come  to  lie  in  different  planes.  Thus, 
in  a  longitudinal  section  the  nuclei  are  seen  to  be  placed  in  several 
rows. 

The  development  of  this  type  from  the 
simpler  forms  occurs  when  the  cells  are  too 
crowded  to  retain  their  normal  breadth.  As 
a  result,  they  become  pyramidal,  alternate 
cells  resting  their  bases  or  apices  on  the  base- 
ment membrane.  As  the  nucleus  is  usually 
situated  at  the  broader  portion  of  the  cell, 
the  result  is  that  there  are  two  rows  of  nu- 
clei simulating  a  stratified  epithelium.  Occa- 
sionally there  are  spindle-shaped  cells  wedged  in  between  the  pyra- 
midal cells,  and  as  the  broad  portion  of  these  cells  is  midway 
between  the  basement  membrane  and  external  surface,  a  third  row 
of  nuclei  is  seen  midway  between  the  other  two.  Such  epithelia 
usually  possess  cilia  (portions  of  the  respiratory  passages). 


Fig.  41.  — Diagram 
of  pseudostratified  col- 
umnar epithelium. 


2.  STRATIFIED  EPITHELIUM. 

Should  the  increase  of  the  cells  forming  the  last  type  of  simple 
epithelium  proceed  to  such  an  extent  that  all  the  cells  no  longer 
rest  on  the  basement  membrane,  an  epithelium  is  formed  having  dis- 


84 


THE    TISSUES. 


tinct  layers  of  cells — a  stratified  epithelium.      It  is  clear  that  all  the 
cells  of  a  stratified  epithelium  can  not  be  equally  well  nourished  by 
the    blood-supply    from    the    vessels    in    the 
highly    vascular    connective    tissue    beneath. 
The  middle  and  outer  layers  of  cells  accord- 
ingly  suffer.      The   deeper   layers   are   much 
better  nourished,  and  as  a  consequence  their 
cells   increase  much  more  rapidly  than  those 
above  ;     they    push    outward,    replacing    the 
superficial    cells    as    fast  as    they   die   or  are 
thrown    off      The    proliferation   of  cells  in   a 
stratified  epithelium  occurs,  therefore,  chiefly 
in  its  basal  layers. 
{a)  Stratified  Squamous   Epithelium. — Stratified   squamous 
epithelium  with  superficial  flattened  cells  forms  the  epidermis  with 
its  continuations  into  the  body,  as,  for  instance,  the  walls  of  the  oral 
cavity   and  the   esophagus,  the  epithelium  of  the  conjunctiva,  the 
vagina,  the  external  auditory  canal,  and  the  external  sheath  of  the 
hair  follicles. 

The  cells  of  the  basal  layer  are  here  mostly  cubic-cylindric. 
Then  follow,  according  to  the  situation  of  the  epithelium,  one  or 
more  layers  of  polyhedral  cells,  which  become  gradually  flattened 
toward    the  surface,   the    outer- 


Fig.  42. — Schematic 
diagram  of  stratified  pave- 
ment epithelium. 


^J^. 

^^1 


f- 


most   layers    consisting   of   thin 
plate-like  cells. 

In  stratified  squamous  epi- 
thelia,  where  the  outer  cells  be- 
come horny  (as  in  the  skin),  the 
stratification  is  still  more  special- 
ized. Here  layers  are  inserted 
in  which  the  horny  or  chitinous 
substance  is  gradually  formed, 
although  the  cells  do  not  be- 
come chitinous  until  the  super- 
ficial layers  are  reached. 

Especially  characteristic  of 
stratified  squamous  epithelium  is 
the  arrangement  of  the  connec- 
tive tissue  on  which  this  epithe- 
lium rests.  There  are  cone-like 
projections,  known  as  papillcs, 
arising  from  the  connective  tissue 
beneath  the  epithelium,  project- 
ing into  the  latter  in  such  a  way  that  on  cross-section  the  junction 
of  the  two  tissues  appears  as  a  wave-like  line.  These  papillae  not 
only  serve  to  fasten  the  epithelium  more  firmly  to  the  connective  tissue 
below,  but  influence  very  favorably  the  nourishment  of  the  former  by 
allowing  a  greater  number  of  its  basal  cells  to  approximate  the  under- 


Fig.  43. — Cross  -  section  of  stratified 
squamous  epithelium  from  the  esophagus 
of  man. 


EPITHELIAL   TISSUES. 


85 


lying  blood-capillaries.  The  pyramidal  extensions  of  the  epithelium 
between  the  papillse  are  designated  interpapillary  epithelial  processes. 
In  regions  where  the  stratified  squamous  epithelium  consists  of 
manylayers,  the  prickle  cells,  intercellular  bridges,  and  the  inter- 
cellular  spaces  are  especially  well  developed.  These  spaces  facili- 
tate the  passage  of  the  lymph-plasma  to  the  more  superficial  layers 

of  cells. 

{b)  Transitional  Epithelium. — Transitional  epithelium  is  a 
stratified  epithelium  occurring  in  the  pelvis  of  the  kidney,  the  ure- 
ters bladder,  and  the  posterior  portion  of  the  male  urethra.  It  is 
com'posed  of  four  to  six  layers  of  cells  and  rests  on  a  connective 
tissue  free  from  papillae.  In  sections  the  cells  of  the  deeper  layers 
appear  to  be  of  irregularly  columnar,  cubic  or  triangular  shape.   The 


-    -^ 


-?fei             .^ 

t 
^      % 

t&^ 

<^ 

■5  r. 

t- 

i      <.' 

*(J  «■'"   ^    (r<t      , 

-/•         —         ^ 

«        '3 

*^  n. ''-  %  ^ 

^ 

■4  i 

c  "" 

■p 

'   "^                'Xti^M   ^      C 

-    -5,    ', 

'  >  =^  >-  *,     ^ 

H- 

0.                   ^ 

tS® 

Fig.  44. — Isolated  transitional  epithe- 


Fig.  45 Cross-section  of  transitional 


lial  cells  from  the  bladder  of  man  :  a,  b,       epithelium  from  the  bladder   of   a  youn^ 
c,  d.  Large  surface  cells,  c  and  d  presenting       child, 
the  pitted  undersurface  ;  e,  variously  shaped 
cells  from  the  deeper  layers. 

cells  forming  the  superficial  layer  are  large,  somewhat  flattened  cells, 
with  convex  free  surfaces,  often  possessing  two,  sometimes  three, 
nuclei.  They  cover  a  number  of  the  cells  of  the  layer  just  beneath 
them,  their  under  surfaces  being  pitted  to  receive  the  upper  ends  of 
the  deeper  cells.  In  teased  preparations  the  cells  of  the  deeper 
layers  appear  very  irregular,  often  showing  ridges  or  variously 
shaped  processes.     (See  Fig.  44.) 

{c)  Stratified  Columnar  Epithelium.— In  this  type  the  super- 
ficial layer  consists  of  columnar  cells,  the  basal  ends  of  which  are 
usually  somewhat  pointed,  or  may  branch.  The  deeper  cells,  which 
may  be  arranged  in  one  or  more  layers,  are  of  irregular,  triangular, 
polyhedral,  or  spindle  shape.  It  is  found  in  the  larger  gland  ducts, 
olfactory  mucous  membrane,  palpebral  conjunctiva,  portions  of  the 


S6 


THE    TISSUES. 


male  urethra  and  the  vas  deferens,  and  in  certain  regions  of  the 
larynx. 

The  ciliated  variety  of  this  epithelium  differs  from  the  foregoing 
in  that  the  superficial  columnar  cells  are  provided  with  cilia.  Strati- 
fied ciliated  columnar  epithelium  is  found  in  the  respiratory  portion 


Fig.  46. — Schematic  dia- 
gram of  stratified  columnar  epi- 
thelium. 


Fig.  47- — Ciliated  cells  from  the  bronchus  of  the 
dog,  the  left  cell  with  two  nuclei ;  X  ^oo- 


of  the  nose,  laiynx,  trachea,  and  larger  bronchi,  in  the  Eustachian 
tube,  epididymis,  and  a  portion  of  the  vas  deferens. 

All  epithelial  cells  are  probably  joined  together  by  short  pro- 
cesses forming  intercellular  bridges,  the  lymph  supplying  them  with 
nourishment  circulating  in  the  intercellular  spaces  thus  formed. 
Toward  the  surface,  these  intercellular  spaces  are  roofed  over,  thus 
preventing  the  escape  of  the  fluid.  When  seen  from  the  surface, 
epithelia  treated  by  certain  methods  (iron-hematoxylin)  show  the 
cells  joined  together  by  very  minute,  clearly  defined  and  continuous 

Goblet  cell. 


—Cilia. 


Fig.  48. — Cross-section  of  stratified  ciliated  columnar  epithelium  from  the 
trachea  of  a  rabbit. 


cement-lines.  Bonnet  has  called  them  terminal  ledges  or  baj^s 
(Schlussleisten).  The  function  of  this  structure  would  seem  to 
consist  in  its  power  to  prevent  the  escape  of  lymph  from  the  sur- 
face, and  the  penetration  of  micro-organisms  (M.  Heidenhain,  92  ; 
Bonnet,  95). 


EPITHELIAL    TISSUES. 


87 


3.  GLANDULAR  EPITHELIUM. 

Glandular  eoithelium  is  composed  of  epithelial  cells  differen- 
tiated so  as  to  possess  the  power  of  elaborating  certain  compounds 
or  substances  which  are  finally  given  off  from  the  cells  in  the  form 
of  secretions.  Those  substances  which  form  the  essential  constitu- 
ents of  such  secretions  appear  in  the  protoplasm  of  the  majority  of 
glandular  cells,  in  the  intervals  of  secretory  activity,  in  the  form  of 
smaller  and  larger  granules  which  may  be  discharged  from  the 
cells  in  granular  form  or  may  be  changed  into  homogeneous,  viscid 
substances  before  leaving  or  on  leaving  the  cells.  Glandular  epi- 
■thelium  appears  in  the  form  of  isolated  glandular  cells,  scattered 
here  and  there  among  other  epithelial  cells,  in  certain  types  of  epi- 
thelium, or  as  smaller  or  larger  aggregations  of  glandular  cells, 
possessing  definite  and  typical   arrangement  and  associated  with 


Fig.  49.— Goblet  cells  from  the  bronchus  of  a 
dog.  The  middle  cell  still  possesses  its  cilia  ;  that  to 
the  right  has  already  emptied  its  mucous  contents 
(collapsed  goblet  cell)  ;   X  600. 


Fig.  50. — A  mucus-secret- 
ing cell  (goblet  cell),  showing 
secretory  granules,  situated  be- 
tween two  epithelial  cells. 
From  the  epithelium  of  the  large 
intestine  of  man. 


other  tissues— connective  tissue,  blood-  and  lymph-vessels,  nerve 
tissue— to  form  structures  or  organs  known  as  secreting  glands. 

Unicellular  Glands.— Isolated  glandular  cells,  which  we  may 
know  as  unicellular  glands,  are  frequently  met  with  in  the  epithe- 
lium of  the  intestinal  canal  and  respiratory  organs,  where,  owing  to 
their  shape,  they  are  known  as  goblet  cells,  or,  again,  as  mucus 
secreting  cells,  since  their  secretion  is  mucus.  Such  cells  are  in 
the  ordinary  preparation  distinguished  from  the  neighboring  cells 
by  the  fact  that  their  free  ends  appear  clearer  and  are  more  vesicu- 
lar, while  their  basal  portions,  containing  the  nuclei,  are  narrow 
and  pointed.  Closer  examination  generally  reveals  a  fine  proto- 
plasmic network  in  the  clear  portion  of  the  cell,  the  interspaces  of 
which  are  filled  with  the  mucus.      (See  Fig.  49.) 

The  secretion  is,  however,  elaborated  in  the  cell-protoplasm  in 


THE    TISSUES. 


Lumen  of 
gland. 


Gland-cells. 


the  form  of  rather  coarse  granules,  which  may  be  as  large  as  i  3^  ^ 
to  2  fx.  These  granules  are  found  in  a  hyaline  substance,  from 
which  they  are  probably  formed,  which  substance  is  found  in  the 
interspaces  of  a  protoplasmic  network  with  relatively  wide  meshes 
(Langley).  The  granules  as  they  develop  and  enlarge  distend  the 
free  portions  of  the  cells.  They  are  eventually  extruded  from  the 
cells,  probably  in  the  form  of  granules,  as  granules  identical  with 
those  found  in  the  cells  are  found  in  the  lumina  of  intestinal  glands 
in  well-fixed  material.  After  the  extrusion  of  the  secretion  the 
cell  collapses,  and  may  again  assume  a  secretory  function  by  the 
elaboration  of  new  granules.      (See  Fig.  50.) 

Multicellular  glands  originate  by  the  metamorphosis  of  a  num- 
ber of  adjacent  cells  into  glandular  cells.  This  is  usually  accom- 
panied by  a  more  or  less 
marked  dipping  down  of 
the  epithelial  layer  into 
the  underlying  connective 
tissue.  The  glandular  cells 
are  generally  arranged  in  a 
single  layer,  and  rest  on  a 
delicate  membrane,  known 
as  the  basement  membrane 
(membrana  propria);  out- 
side of  this  there  is  found 
fibrous  connective  tissue, 
containing  the  terminal 
ramifications  of  capillaries 
and  lymph-spaces  and  of 
nerve-fibers.  The  simplest 
form  of  such  an  invagina- 
tion is  a  cylindrical  tube  or 
a  small  sac  (known  as  an 
alveolus)  lined  entirely  by 
glandular  cells.  A  further 
differentiation  may  take 
place  in  that  all  the  invaginated  cells  do  not  assume  a  secretory  func- 
tion, those  at  the  upper  portion  of  the  tube  or  sac  forming  the  lining 
membrane  of  an  excretory  duct.  The  originally  uniform  tube  or  sac 
is  thus  differentiated  into  a  duct  and  a  secretory  portion.  Multi- 
cellular glands  may  lie  entirely  within  the  epithelium,  and  are  then 
known  as  intra-epithellal  glands,  in  contrast  to  the  extra-epithelial 
or  ordinary  type,  the  greater  part  of  which  lies  imbedded  in  the 
underlying  connective  tissue.  Glands  of  the  former  type  have  been 
studied  in  amphibian  larvae,  and,  according  to  Sigmund  Mayer, 
occur  also  in  the  epididymis,  conjunctiva,  etc.,  of  mammals. 

General  Consideration  of  the  Structure  and  Classification 
of  Glands. — Since  glandular  tissue  is  composed  almost  wholly  of 
epithelial  cells,  it  may  not  be  out  of  place  to  consider  at  this  time 


Muse,  mucosae. 


Fig.  51. — Simple  tubular  glands.  Lieber- 
kühn's  glands  from  the  large  intestine  of  man. 
Sublimate  fixation  ;   X  90- 


EPITHELIAL    TISSUES.  89 

the  classification  of  glands.  The  fuller  consideration  of  these 
structures  will,  however,  be  deferred  to  a  later  time.  In  the  classi- 
fication here  given  we  have  been  guided  by  that  presented  by 
Maziarski,  in  an  observation  on  the  structure  and  classification  of 
glands,  based  on  a  series  of  reconstructions  with  the  Born  wax- 
plate  method  and  comprising  nearly  all  the  important  glandular 
structures  of  the  human  body.  In  brief,  it  may  be  stated  that  the 
variation  in  glandular  types  affects  principally  the  secretory  portions 
of  glands,  while  the  excretory  ducts  are  more  or  less  uniform. 
Glands  are  classified,  according  to  their  shape,  into  tubular  and 
alveolar  glands;  each  of  these  types  is  further  divided  into  simple 
and  branched  tubular,  and  simple  and  branched  alveolar  glands. 
In  certain  glands  tubules  and  alveoli  unite  to  form  the  secretory 


Fig.   52. — Excretory  ducts  Fig.    53. — Lumina    of    the    secreting    portion 

and    lumina    of    the     secretory  of  a    reticulated    tubular   gland ;    from    the    human 

portion  of  a  compound  tubular  liver.      Chrome-silver  preparation  ;   X  '^o. 
gland.       Lingual    gland    of   the 
rabbit.      Chrome-silver  prepara- 
tion ;   X  215. 

portion;  such  glands  are  known  as  tubulo -alveolar  glands.      They 
may  also  be  simple  or  branched. 

Tubular  Glands.— In  a  tubular  gland  the  secreting  portion 
consists  of  a  longer  or  shorter  tubule,  which  may  be  relatively 
straight  or  variously  twisted  or  coiled,  one  end  of  which  ends 
blindly  while  the  other  end  opens  on  a  free  surface  or  into  a  duct. 
The  blind  ends  of  the  tubules  of  tubular  glands  often  present  more 
or  less  well-marked  enlargements.  Simple  tubular  glands  consist 
of  a  single  tubule,  which  may  be  lined  throughout  by  secretory 
epithelium  or  may  be  differentiated  into  a  portion  lined  by  secretory 
epithelium  and  a  portion  lined  by  a  non-secretory  epithelium  form- 
ing a  duct.  An  increase  of  the  secretory  surface  of  tubular  glands 
is  obtained  in  one  of  the  following  ways: 


go 


THE    TISSUES. 


1.  Coiled  Tubular  Gland. — The  secreting  portion  of  the  tubule 
may  be  coiled  up  into  a  compact  mass ; 

2.  Simple  Branched  Tubular  Glands.  — Several  tubules,  which 
may  be  either  branched  or  unbranched,  and  which  may  vary  greatly 
in  length,  may  unite  in  one  duct,  which  carries  to  the  surface  the 
secretion  of  all  the  tubules  connected  with  it ; 

3.  Compound  Branched  Tubidar  Glands. — Glands  of  this  type 
consist  of  a  varying  number  of  simple  branched  tubular  glands,  the 
ducts  of  which  unite  to  form  a  common  duct  (Fig.  52); 


Fig.  54.— Schematic  diagram  of  glandular  classification  :  i,  Simple  tubular  gland; 
2,  simple  tubular  gland  with  coiled  secreting  portion ;  3,  4,  5>  types  of  simple  branched 
tubular  glands;  6,  compound  branched  tubular  gland;  7,  8,  types  of  simple  branched 
tubulo-alveolar  glands  ;  9,  simple  alveolar  gland;  10,  II,  types  of  simple  branched  alve- 
olar glands  ;  12,  compound  branched  alveolar  gland  ;  13,  type  of  follicular  gland  ;  14, 
reticular  gland,  the  shaded  portions  representing  anastomosing  tubules. 

4.  Reticulated  Tubidar  Glands. — In  certain  of  the  branched 
tubular  glands  the  secreting  tubules  anastomose  with  each  other, 
forming  a  reticulated  gland  (Fig.  53) ; 

5.  Tubulo-alveolar  Gland. — The  secreting  surface  of  tubular 
glands  may  be  further  increased  by  the  formation  of  small  and 
variously  shaped  protuberances  or  saccules,  known  as  alveoli, 
which  may  be  situated  at  the  end  or  on  the  sides  of  the  tubules, 
and   are   lined  by  secretory   epithelium    and  empty  the    secretion 


EPITHELIAL    TISSUES. 


91 


formed  in  them  into  the  tubules  with  which  the\^  are  connected. 
We  have  thus,  in  addition  to  the  several  t\-pes  of  tubular  glands 
above  mentioned  :  Simple  tubulo-alveolar  glands,  simple  branched 
tubulo-alveolar  glands,  and  compound  branched  tubulo-alveolar 
glands. 

Alveolar  Glands. — In  the  alveolar  glands  the  secreting  com- 
partments have  the  form  of  variousl\-  shaped  vesicles  or  saccules, 
known  as  alveoli,  lined  by  secretory  epithelium,  which  communi- 
cate with  narrow  tubules  of  var}-ing  length  and  lined  b}-  non- 
secretory  epithelium,  which,  form  the  ducts.  Alveolar  glands  are 
classified  as : 

1.  Simple  alveolar  glands,  consisting  of  a  single  alveolus  which 
communicates  with  the  surface  by  means  of  a  narrow  duct. 

2.  Simple  Brancked  Alveolar  Glands. — In  this  type  a  varying 
number  of  alveoli  are  united  through  their  respective  ducts  to  a 
larger  duct  which  reaches  the  surface. 

3.  Compound  Branched  Alveolar  Glands. — Glands  of  this  t>^pe 
consist  of  a  varying  number  of  simple  branched  alveolar  glands 
united  by  a  common  duct. 

4.  Follicular  Glands. — Glands  of  this  t\'pe  may  be  classed  under 
alveolar  glands,  since  they  consist  of  numerous  closed  alveoli  or 
follicles,  of  round,  oval,  or  even  irregular  shape,  which  do  not 
communicate  with  a  duct  system. 

The  main  features  of  this  classification  of  glands  are  portra}-ed 
in  the  accompanying  diagram  (Fig.  54). 

According  to  the  above  description  multicellular  glands  may 
be  classified  as  follows  : 

'  I.  Simple  tubular  glands:   cn-pts  of  Lieberkühn,  the  majority  of 
/  the  sweat  glands. 

\    2.  Simple  branched  tubular  glands:  fundus  glands  of    stomach, 
Tubular   glands.  '^^  majorit}-  of  the  pyloric  glands,  uterine  glands. 

'3.  Compound  branched  tubular  glands  :  kidnevs,   testis,   lachry- 
/  mal  glands,  serous  glands  of  mucous  membranes. 

\    4.  Reticulated  tubular  glands  :   Liver  (fully  developed  in  mam- 
mals). 

(I.  Simple  tubulo-alveolar  glands  :   certain  of  the  pyloric  glands. 

2.  Simple  branched  tubulo-alveolar  glands  :   Littre's  glands,  cer- 
tain of    the   sweat  glands,   and  modified   sweat  glands 
glands.              \  (circumanal    and  axillary   glands,    ceruminous   glands, 

'  )  cilian,-  glands). 

I    3.  Compound    branched    tubulo-alveolar    glands :    manv  mucous 
'  glands,  Brunner's  glands,  prostate,  lung. 

1.  Simple  alveolar  glands:  the  smallest  sebaceous  glands,  the 
skin  glands  of  amphibia. 

2.  Simple  branched  alveolar  glands :  sebaceous  glands,  Meibo- 
mian glands. 

3.  Compound    branched    alveolar    glands :     pancreas.    mammar%' 
Alveolar    glands.  gl=^n<i'  serous  salivary  glands — in  the  latter,  however,   a 

portion  of  the  duct  system  possesses  secretory  function 
(Maziarski). 

4.  Follicular  glands :  ovan.-,  hypophysis,  thyroid  (according  to 
Streitf,  certain  of  the  closed  follicles  of  the  th%Toid  have 
a  tubular  form,  others  show  secondar)"  alveolar  enlarge- 
ments on  the  primär)'  follicles). 


92  THE    TISSUES. 

The  secretory  epithelium  of  the  various  types  of  glands  rests 
upon  a  thin  membrane  (membrana  propria),  which  has,  according  to 
some  authors,  a  connective-tissue  origin,  while,  according  to  others, 
it  is  the  product  of  the  glandular  cells  themselves.  In  some  cases 
it  appears  structureless,  in  others  a  cellular  structure  can  be  distin- 
guished; in  the  latter  case  the  cells  are  flattened,  with  very  much 
flattened  nuclei,  and  show  irregular  outlines.  Macroscopically, 
compound  glands  present  a  more  or  less  lobular  structure, 
the  separate  lobules  being  held  together  by  connective  tissue. 
In  the  immediate  neighborhood  of  the  gland  and  its  larger  lobes, 
the  connective  tissue  is  thickened  to  form  the  so-called  tunica 
albuginea  or  capsule.  In  this  fibrous-tissue  sheath  are  found  numer- 
ous blood-vessels  which  penetrate  between  the  lobes  and  lobules  of 
the  gland  and  form  a  dense  capillary  network  about  the  tubules  and 
alveoli  immediately  beneath  the  membrana  propria.  Nerve-fibers 
are  also  plentiful. 

Remarks  on  the  Process  of  Secretion. — The  gland-cell 
varies  in  its  microscopic  appearance  according  to  its  functional  con- 
dition. In  the  great  majority  of  the  glandular  epithelial  cells  the 
essential  constituents  of  the  secretion  are  stored  in  the  cell  in 
the  form  of  secretory  granules,  in  others  in  vacuoles  which  are 
filled  with  the  secretion.  The  secretory  process  varies.  In  one 
case  the  cell  remains  intact  throughout  the  process  (salivary  glands)  ; 
in  another  a  portion  of  each  cell  is  used  up  in  the  production  of 
the  secretion,  only  the  basal  portion  containing  the  nucleus  being 
preserved.  When  this  occurs,  the  upper  part  of  the  cell  is  recon- 
structed from  the  remaining  basal  portion,  and  the  cell  is  ready  to 
renew  the  process  (mammary  glands).  In  a  third  type  the  whole 
cell  is  destroyed,  and  is  replaced  by  an  entirely  new  cell  (sebaceous 
glands). 

4.  NEURaEPITHELIUM. 

In  certain  of  the  organs  of  special  sense  (inner  ear  and  taste-buds) 
the  epithelial  cells  about  which  the  nerves  terminate  undergo  a  high 
degree  of  specialization.  This  differentiation  is  more  apparent  in  the 
outer  portions  of  these  cells,  resulting  in  the  formation  of  one  or  sev- 
eral stiff",  hair-like  processes,  which  appear  especially  receptive  to 
stimuli.  Such  cells  are  known  as  neuro-epithelial  cells.  In  the 
epithelia  in  which  they  occur  they  are  surrounded  by  supporting 
or  sustentacular  cells. 


5.  MESOTHELIUM  AND  ENDOTHELIUM. 

The  pleural,  pericardial,  and  peritoneal  cavities  are  lined  by 
a  single  layer  of  flattened  epithelioid  cells  which  develop  from  the 
mesothelium  lining  the  primitive  body  cavity  (celom).  For  this 
reason,  as  has  been  suggested  by  Minot  (90),  the  term  mesothelium 
may  with  propriety  be  applied  to  this  layer  in  its  developed  condi- 


EPITHELIAL    TISSUES. 


93 


tion.  In  silver  nitrate  preparations,  in  which  the  boundaries  of  these 
cells  are  brought  to  view,  they  appear  as  much  flattened  cells, 
resembling  those  of  squamous  epithelium,  with  faintly  granular 
protoplasm,  possessing  flattened,  oval,  or  nearly  round  nuclei. 
These  cells  are  of  polyhedral  shape,  and  appear  to  be  united  into 
a  single  layer  by  a  small  amount  of  intercellular  cement  substance. 
The  borders  of  these  cells  may  be  quite  regular  or  slightly  wavy 
(Fig.  55);  more  often  they  are  serrated  (Figs.  56,  57).  According 
to  Kolossow,  who  has  investigated  these  cells  by  means  of  special 
methods  devised  by  him,  the  mesothelial  cells  are  said  to  be  made 


./^'^'■\h  \ 


n 


Fig.  55. — Mesothelium  from  peri- 
cavdium  of  rabbit.  Silver  nitrate  prepar- 
ation, stained  in  hematoxylin. 


Fig.  56. — Mesothelium   from  mesentery 
of  rabbit. 


■"  Nucleus. 

.  Cell  boundary. 


Fig.  57- — Mesothelium  from  peritoneum  of  frog;   X  4°°- 


up  of  two  quite  distinct  portions  :  a  superficial,  homogeneous  cell- 
plate,  beneath  which  is  found  a  finely  granular  protoplasm  contain- 
ing the  nucleus.  These  two  portions  are  intimately  united  to  form 
a  single  cell.  The  outlines  of  the  superficial  cell-plates  are  figured 
in  the  accompanying  illustrations.  The  protoplasmic  portion  of 
one  cell  unites  with  that  of  contiguous  cells  by  means  of  proto- 
plasmic branches,  between  which  are  found  intercellular  spaces. 
These  intercellular  spaces  are  here  and  there  indicated  in  siher 
nitrate  preparations,  forming  what  are  known  as  stigmata  and 
stomata,  which  are  looked  upon  by  certain  writers  as  representing 


94 


THE    TISSUES. 


openings  between  the  mesothelials  cells  through  which  fluids  and 
solid  particles  may  pass  into  underlying  lymph  spaces.  They  are, 
however,  now  generally  regarded  as  artefacts. 

Endothelial  cells  are  differentiated  mesenchymal  cells.    They  line 
the  blood-  and  lymph-vessels  and  lymph-spaces  (arachnoidal  anG 


Fig.  58.  — Mesothelium  covering  posterior  abdominal  wall  of  frog.      Stained  with  silver 

nitrate  and  hematoxylin. 


Fig.  59.  — Endothelial  cells  from  small  artery  of  the  mesentery  of  a  rabbit, 
silver  nitrate  and  hematoxylin. 


Stained  with 


synovial  spaces,  anterior  chamber  of  the  eye,  bursae,  and  tendon 
sheaths).  Endothelial  cells  are  in  structure  like  those  of  the  meso- 
thelium. In  blood-  and  lymph-vessels  they  are  of  irregular,  oblong 
shape,  with  serrated  borders.  The  boundaries  of  these  cells  are 
clearly  brought  out  by  silver  nitrate. 


TECHNIC. 

Epithelium  may  be  examined  in  a  fresh  condition.  The  sim- 
plest method  consists  in  placing  some  saliva  under  a  cover-glass  and 
examining  it  with  a  moderate  power.  In  it  will  be  found  a  number  of 
isolated  squamous  epithelial  cells,  suspended  in  the  saliva  singly  and  in 
groups.  The  cells  that  are  cornified  still  show  the  nucleus  and  a  small 
granular  area  of  protoplasm. 


EPITHELIAL    TISSUES.  95 

In  order  to  examine  isolated  epithelial  cells  of  organs,  it 
is  necessary  to  treat  the  epithelial  shreds  or  whole  epithelial  layers  with 
the  so-called  isolating  or  maceration  fluids.  These  are:  (i)  Iodized 
serum;  (2)  very  dilute  osmic  acid  (0.1%  to  0.5%)  ;  (3)  very  weak 
chromic  acid  solution  (about  1:5000  of  water)  ;  (4)  0.5%  or  1%  solution 
of  ammonium  or  potassium  bichromate  ;  and,  above  all,  the  one-third 
alcohol  recommended  by  Ranvier  (28  vols,  absolute  alcohol,  72  vols. 
distilled  water).  The  mixture  recommended  by  Soulier  (91),  consist- 
ing of  sulphocyanid  of  potassium  or  ammonium,  and  the  mixture  of 
Ripart  and  Petit  serve  the  same  purpose.  All  these  solutions  are  used  by 
allowing  a  quantity  of  the  isolation  fluid  to  act  upon  a  small  fresh  piece 
of  epithelium  for  from  twelve  to  twenty-four  hours,  according  to  the  tem- 
perature of  the  medium  and  quality  of  the  tissue.  As  soon  as  the  isola- 
tion fluid  has  done  its  work,  it  is  easy  to  complete  the  isolation  of  the 
cells  by  shaking  the  specimen  or  teasing  it  with  needles.  Separation  of 
the  elements  may  be  accomplished  either  in  the  isolation  solution  itself  or 
in  a  so-called  indifferent  fluid,  or  in  gum-glycerin.  The  macerated  pre- 
paration may  be  stained  in  a  hematoxylin  or  carmin  solution  before  teas- 
ing and  mounting  in  gum-glycerin. 

The  movement  of  the  cilia  can  be  observed  in  mammalian  tissues 
by  scraping  the  epithelium  from  the  trachea  with  a  scalpel  and  examining  it 
in  an  indifferent  fluid.  As  the  ciliated  epithelium  of  mammals  is  very 
delicate  and  sensitive,  specimens  with  a  longer  duration  of  ciliary  move- 
ment are  more  desirable.  They  can  be  obtained  by  using  the  mucous 
membrane  from  the  palate  of  a  frog  (examine  in  normal  salt  solution). 
Particularly  large  epithelial  cells,  as  well  as  very  long  cilia,  are  found  on 
the  gill-plates  of  mussels  or  oysters. 

In  order  to  study  the  relations  of  mesothelial  and  endothe= 
lial  cells,  the  silver  method  is  the  most  satisfactory.  The  outlines  of  the 
mesothelial  cells  may  be  clearly  brought  out  by  placing  pieces  of  the  peri- 
cardium, central  tendon  of  the  diaphragm,  or  the  mesentery  in  a  o.  75  '^  to 
I  ^  solution  of  silver  nitrate.  Before  placing  in  this  solution,  they  should 
be  rinsed  in  distilled  water  in  order  to  remove  any  adherent  foreign  bodies, 
such  as  blood-corpuscles,  etc.  In  this  solution  they  remain  until  opaque, 
which  occurs  in  from  ten  to  fifteen  minutes.  They  are  then  again  rinsed 
with  distilled  water,  in  which  they  are  exposed  to  sunlight  until  thty 
begin  to  assume  a  brownish-red  color.  Once  again  they  are  washed  with 
distilled  water,  and  either  placed  in  glycerin,  in  which  they  may  be 
mounted,  or  dehydrated  and  mounted  in  Canada  balsam,  according  to  the 
usual  methods.  The  margins  of  the  cells  subjected  to  this  treatment  will 
appear  black. 

Endothelial  cells  may  be  demonstrated  after  the  following  method  : 
A  small  mammal  (rat,  Guinea-pig,  rabbit,  or  cat)  is  narcotized.  Before 
the  heart's  action  is  completely  arrested,  the  thorax  is  opened  and  the 
heart  incised.  As  soon  as  the  blood  stops  flowing,  a  cannula  is  inserted 
and  tied  in  the  thoracic  aorta  a  short  distance  above  the  diaphragm,  and 
50  to  80  c.c.  of  a  i^  aqueous  solution  of  si}ver  nitrate  injected  through 
the  cannula.  About  fifteen  minutes  after  the  injection  of  the  silver  nitrate 
solution,  there  is  injected  through  the  same  cannula  100  to  150  c.c.  of  a 
4%  solution  of  formalin  (formalin  10  parts,  distilled  water  90  parts). 
The  abdominal  cavity  is  then  opened,  loops  of  the  intestine  with  the- 
attached  mesentery  removed  and  placed  in  a  4%  solution  of  formalin,  in 
which  the  tissue  is  exposed  to  the  sunlight.     As  soon  as  the  reduction  of 


96  THE    TISSUES. 

the  silver  nitrate  has  taken  place,  which  is  easily  recognized  by  the  reddish- 
brown  color  assumed  by  the  tissues,  the  mesentery  is  divided  into  small 
pieces,  dehydrated  first  in  95%,  then  in  absolute  alcohol,  cleared  in  oil 
of  bergamot,  and  mounted  in  balsam.  As  a  rule,  the  mesothelial  cells 
covering  the  two  surfaces  of  the  mesentery,  and  the  endothelial  cells 
lining  the  arteries,  veins,  and  capillaries  are  clearly  outlined  by  the 
reduced  silver  nitrate. 

If  desired,  the  tissue  may  be  further  stained  in  hematoxylin  (we  have 
used  Böhmer' s  hematoxylin  solution)  or  in  a  carmin  solution  after  dehy- 
dration in  95%  alcohol,  after  which  they  are  dehydrated,  cleared,  and 
mounted  in  balsam.  In  preparations  made  after  this  method  the  endo- 
thelial cells  are  outlined  by  fine  lines  of  dark  brown  or  black  color. 

Silver  nitrate  may  also  be  dissolved  in  a  2  ^  to  3  %  solution  of  nitric 
acid,  in  osmic  acid,  and  various  other  fluids.  Stratified  epithelia  can 
also  be  impregnated  with  silver  nitrate,  but  only  after  prolonged  immer- 
sion. They  are  exposed  to  sunlight  after  sectioning  on  the  freezing 
microtome,  or  after  hardening  and  imbedding,  followed  by  sectioning. 
After  the  reduction  of  the  silver  the  sections  are  dehydrated  and  mounted 
in  balsam. 

Kolossow  has  devised  the  following  excellent  method  for  demon- 
strating intercellular  bridges  :  Fine  membranes,  or  even  minute  frag- 
ments of  previously  fixed  tissues,  are  placed  for  about  a  quarter  of  an  hour 
in  a  0.5^  to  i^  osmic  acid  (or  in  a  mixture  composed  of  50  c.c.  abso- 
lute alcohol,  50  c.c.  distilled  water,  2  c.c.  concentrated  nitric  acid,  and 
I  to  2  gm.  osmic  acid)  and  then  into  a  10^  aqueous  solution  of  tannin 
for  five  minutes,  or  into  a  developer  consisting  of  the  following :  water, 
450  c.c.  ;  85^  alcohol,  100  c.c..;  glycerin,  50  c.c.  ;  purified  tannin, 
30  gm.,  and  pyrogallic  acid,  30  gm.  In  the  latter  case  they  are  subse- 
quently rinsed  in  a  weak  solution  of  osmic  acid,  washed  with  distilled 
water,  and  then  carried  over  into  alcohol. 

There  are,  of  course,  special  methods  of  fixing  and  subsequently 
examining  epithelial  structures ;  these,  and  the  methods  of  examining 
gland  tissue,  will  be  discussed  in  the  chapters  devoted  to  the  various 
organs. 

B.  THE  CONNECTIVE  TISSUES. 

In  the  connective  tissues,  the  intercellular  substance  gives  char- 
acter to  the  tissue,  the  cellular  elements  forming  a  less  conspicuous 
portion.  In  their  fully  developed  condition  some  of  the  members 
of  the  connective -tissue  group  are  only  slightly  altered  from  em- 
bryonic connective  tissue.  In  other  members  there  are  developed, 
in  less  or  greater  number,  fibers,  known  as  connective -tissue  fibers, 
thus  forming  reticular  connective  tissue  and  the  looser  and  denser 
forms  of  fibrous  connective  tissue.  A  more  marked  condensation 
of  the  intercellular  substance  is  observed  in  cartilage;  and  in  bone 
and  dentin  a  still  greater  degree  of  density  is  obtained  by  the  de- 
position of  calcareous  salts  in  the  intercellular  matrix.  In  the  dif- 
ferent types  of  connective  tissue  the  cellular  elements  are  morpho- 
logically very  similar.  The  role  played  by  the  connective  tissues 
in  the  economy  of  the  body  is  largely  passive,  depending  on  their 


THE    CONNECTIVE    TISSUES. 


97 


nhvsical  properties.     Bone  and  cartilage  serve  as  supporting  tissues ; 
the   looser   fibrous   tissues  for  binding  and  holding  the  organs  and 
parts  of  organs  firmly  in  place.      The  denser  fibrous  connective  tis- 
sues come  into  play  where  strength  and  pliability  are  desired,  as  in 
licraments   or  else  are  used  in  the  transmission  of  muscular  force,  as 
in'' tendons      Another  important  characteristic  of  connective  tissue  is 
that  its  various  members  are   capable  of  undergoing  transformation 
into  wholly  different  types ;   bone,  for  instance,  being  developed  from 
fibrous  connective  tissue  and  from  cartilage.      Certain  structures  are 
represented  bv  different  members  of  the  connective-tissue  group  in 
the  different  classes  of  vertebrates.      In  certain  fishes  the  skeleton  is 
cartilacxinous,  and  in  certain   birds   the  leg  tendons  are  formed  ot 
osseous  tissue,  etc.     The  connective  tissues  receive  their  nutrition 
from    the     lymph.       In     the 
denser  connective  tissues  this 
permeates  the  tissues  through 
clefts  or  spaces  in  the  ground- 
substance,  in  which  the  con- 
nective-tissue cells  are  found 
and    which     are     united     by 
means    of   fine   canals   into  a 
canalicular    system.       In    the 
looser   fibrous  tissues  and  in 
mucous  connective  tissue  the 
system  of  lymph-channels  is 
not  present ;  here  the  lymph 
seems    to    pass    through    the 
ground-substance. 

Certain  connective-tissue 
cells  have  the  function  of 
producing  fat.  In  various 
parts  of  the  body,  masses  of 
fat    tissue    are     formed    as    a 


-Jr— r Ji —  Cell  pro- 


—   Nucleus. 


^  Li 


'ff'^^"^: 


M4 


Fig.    60.— Mesenchymatous    tissue   from   the 
subcutis  of  a  duck  embryo  ;   X  ^5°- 


protection    to    various  organs 

and  as  a  reserve  material  upon  which  the  body  can  call  when  ne- 
cessary This  type  can  hardly  be  considered  a  separate  class  ot 
connective  tissues,  as  it  can  be  demonstrated  that  it  is  merely  modi- 
fied connective  tissue,  and  can  occur  wherever  the  latter  is  lound. 
Finally  certain  elements  of  the  middle  germinal  layer  are  capable 
of  producing  colored  substances  known  as  pigments.  To  this  class 
belong  the  pigment  cells  and  the  red  blood-corpuscles. 

All  the  members  of  this  group  are  developed  from  the  mesen- 
chyme an  embryonic  tissue  developed  early  in  embryonic  life  from 
the  middle  germ  laver  or  mesoderm.  In  its  early  development  the 
mesenchyme  is  probably  composed  of  individual  cells.  As  develop- 
ment advances  the  protoplasm  of  these  cells  increases,  and  is  united 
by  means  of  the  protoplasmic  branches  formed  by  the  cells  to  form 
a  protoplasmic  complex  known  as  a  syncytium.  The  turther 
7 


98 


THE    TISSUES. 


development  and  differentiation  of  the  syncytium  has  been  described 
in  full  by  F.  P.  Mall,  whose  account  is  here  followed.  As  soon  as 
the  syncytium  is  formed  its  protoplasm  grows  rapidly,  and  appears 
in  large  bands  with  spaces  between  them,  and  with  relatively  few 
nuclei.  In  its  further  development  the  protoplasm  of  the  syncytium 
differentiates  into  a  fibrillar  part,  which  forms  the  main  portion  of 
the  syncytium — the  exoplasm — and  a  granular  part  which  surrounds 


i 

■1 

;;j; 

/'^,;' 

e    ■ 

J,/ 

e 

A 

1 

1 

A' 

-1       \ 

^0' 

/ 

) 

Fig.  6l. — Schematic  diagram  given  to  show  the  development  of  the  different  types 
of  connective  tissue  from  the  mesenchyma :  a,  Mesenchymal  cells,  certain  of  which  are 
separate,  others  are  joined  by- protoplasmic  branches;  b,  syncytium  with  large  strands  of 
protoplasm  and  relatively  few  nuclei ;  c,  reticular  tissue, — the  dark  fibers  are  elastic  fibers  ; 
d,  white  fibrous  tissue ;  e,  cartilage;  f,  membranous  bone. 


the  nucleus — the  endoplasm.  The  fibrils  of  the  exoplasm  are  very 
delicate  and  anastomose  freely.  Probably  in  all  the  members  of  the 
connective-tissue  group,  the  so-called  intercellular  substance — 
fibers,  matrix  of  cartilage  and  bone — is  developed  in  or  from  the 
exoplasm,  while  the  cellular  elements  are  differentiated  from  the 
nuclei  and  endoplasm.  The  main  features  of  the  development  of 
the  different  types  of  connective  tissue  are  portrayed,  in  part  schemati- 


THE    CONNECTIVE    TISSUES. 


99 


cally,  in  fig.  6i,  combined  from  a  number  of  figures  illustrating  F.  P. 
Mall's  article  dealing  with  this  subject. 

The  fibers  of  white  fibrous  tissue  develop  in  the  exoplasm,  while 
tiie  endoplasm  containing  the  nuclei  rests  on  the  bundles.  In  cartil- 
age the  ground-substance  or  matrix  is  deposited  into  the  exoplasm 
of  the  syncytium,  the  endoplasm  and  nuclei  forming  the  cartilage 
cells.  In  bone,  the  bone  substance  or  matrix  is  developed  from  the 
exoplasm,  either  by  a  transformation  of  it  or  by  a  deposition  in  it, 
while  the  endoplasm  increases  and  the  nuclei  enlarge  to  form  the 
bone-forming  cells,  the  osteoblasts.  The  reticulum  of  reticular  con- 
nective tissue  is  developed  directly  from  the  exoplasm  of  the  syncy- 
tium, while  the  nuclei  and  endoplasm  are  converted  into  cells  which 
rest  upon  the  reticulum  fibrils. 

The  following  kinds  of  connective  tissue  are  recognized:    (i) 
mucous  connective  tissue,  (2)  reticular  connective  tissue,  (3)  fibrous 
•connective  tissue,  (4)  adipose  tissue,  (5)  cartilage,  (6)  bone. 


Yig,  62. — WTiite  fibrils  and  small  bun- 
dles of  white  fibrils  from  teased  preparation 
of  a  fresh  tendon  from  the  tail  of  a  rat. 


Fig.  62J. — Elastic  fibers  from  the  liga- 
mentum  nuchae  of  the  ox,  teased  fresh  ; 
X  500.  At  a  the  fiber  is  curved  in  a  char- 
acteristic manner. 


The  fibrous  connective  tissues  are  composed  of  a  ground-sub- 
stance or  matrix  in  which  are  imbedded  the  cellular  elements  and 
two  kinds  of  connective-tissue  fibers,  namely,  white  and  elastic 
fibers.  As  the  character  of  the  fibrous  connective  tissue  depends 
largely  on  the  arrangement  of  the  fibers  and  on  the  relative  propor- 
tion of  the  white  and  elastic  fibers,  these  will  be  considered  prior  to 
a  description  of  the  several  types  of  fibrous  connective  tissue. 

W/iiU  Fibers. — White  fibrous  connective  tissue  consists  of  ex- 
ceedingly fine  homogeneous  fibrillse,  cemented  by  a  small  amount 
of  an  interfibrillar  cement  substance  into  bundles  varying  in  size.  In 
the  bundles  these  fibrillae  have  a  parallel  course,  although  the  bun- 
dles are  often  slightly  wavy.  The  fibrillEe  of  white  fibrous  connective 
tissue  vary  in  size  from  0.25  to  i  //,  and  neither  branch  nor  anasto- 
mose. They  become  transparent  and  swollen  when  treated  with 
acetic  acid,  are  not  at  all  or  only  very  slowly  digested  by  pancreatin, 
and  yield  gelatin  on  boiling. 


lOO  THE    TISSUES. 

Elastic  Fibers. — These  are  homogeneous,  highly  refractive,  dis- 
tinctly contoured  fibers,  varying  in  size  from  i  //  to  6  //,  and  in  somd 
animals  are  even  larger.  They  branch  and  anastomose,  and  are  not 
cemented  into  bundles.  When  extended,  they  appear  straight ; 
when  relaxed,  they  show  broad,  bold  curves,  or  are  arranged  in 
the  form  of  a  spiral.  The  broken  ends  of  the  fibers  are  bent  in  the 
form  of  a  hook.  F.  P.  Mall  has  shown  that  elastic  fibers  are  com- 
posed of  two  distinct  substances — an  outer  delicate  sheath  which  does 
not  stain  in  magenta,  and  an  interior  substance  which  is  intensely 
colored  in  this  stain.  The  interior  substance  is  highly  refractive. 
Elastic  fibers  are  not  affected  by  acetic  acid,  but  are  readily  digested 
in  pancreatin  and  less  readily  in  pepsin.  They  yield  elastin  on 
boiling. 

J.  MUCOUS  CONNECTIVE  TISSUE. 

Mucous  connective  tissue  is  a  purely  embryonal  type,  and 
scarcely  represented  in  the  adult  human  body.  It  consists  of 
branched,  anastomosing  cells  imbedded  in  a  ground-substance  which 
gives  a  reaction  for  mucus  and  contains  a  varying  number  of 
white  fibrous  tissue  fibers  which  are  developed  from  a  syncytial 
protoplasm.  The  latter  as  well  as  the  mucous  matrix  are,  directly 
or  indirectly,  the  products  of  the  cells.  During  the  development 
of  the  embryo  this  tissue  is  found  in  large  quantities  in  the  umbilical 
cord,  and  is  here  known  as  Wharton's  jelly.  Mucous  connective 
tissue  is  merely  another  name  for  embryonic  connective  tissue  and  is 
found  as  such  wherever  connective  tissue  develops.  In  the  adult 
it  occurs  in  the  posterior  chamber  of  the  eye  as  the  vitreous  humor. 

2.  RETICULAR  CONNECTIVE  TISSUE. 

Reticular  connective  tissue  is  a  fibrous  connective  tissue  in  which 
the  intercellular  substance  has  disappeared.  The  tissue  is  often 
described  as  being  composed  of  anastomosing  branched  cells,  ar- 
ranged in  the  form  of  a  network  with  open  spaces.  The  obser- 
vations of  Ranvier  and  Bizzozero,  and  more  recently  those  of  Mall, 
have  shown  that  the  framework  of  reticular  tissue  is  composed  of 
very  fine  fibrils  or  bundles  of  fibrils.  These  interlace  in  all  planes 
to  form  a  most  intricate  network,  surrounding  spaces  of  varying  size 
and  shape.  According  to  F.  P.  Mall,  the  fibrils  of  reticular  tissue 
differ  chemically  from,both  the  white  and  elastic  fibers,  although  their 
composition  has  not  been  fully  determined.  Like  white  fibrous 
tissue,  reticular  tissue  is  not  digested  by  pancreatin,  but,  unlike 
white  fibrous  tissue,  it  does  not  appear  to  yield  gelatin  upon  boiling 
in  water,  but  a  mixture  of  gelatin  and  reticulin,  a  substance  identi- 
fied by  Siegfried. 

The  cells  of  reticular  connective  tissue,  which  are  flattened  and 
often  variously  branched,  lie  on  the  reticular  network,  being  often 
wrapped  about  the  bundles  of  fibrils.     Unless  they  are  removed,  the 


THE    CONNECTIVE    TISSUES. 


lOI 


reticulum  has  the  appearance  of  a  network  composed  of  branched 
and  anastomosing  cells. 

Reticular  connective  tissue  is  found  in  adenoid  tissue  and  lymph- 
glands  in  the  spleen,  and  in  the  mucous  membrane  of  the  intestinal 
canal  and  in  these  locations  the  meshes  of  the  reticulum  are  filled  with 
Ivmph-cells  and  other  cellular  elements,  which,  unless  removed, 
ob'^cure  the  reticulum.  Connective-tissue  fibrils  gi\ing  the  same 
reaction  as  those  found  in  the  adenoid  reticulum  are  found  associ- 


Fi^.    6-.— Rencu'-ar   nbers    from   a   tiiin   secdon   of  a  Ivmph-gland,   digested   on    the 
•^'  jjj^g  j^  TDancreatin  and  stained  in  iron-lac -hematoxylin. 

ated  with  white  and  elastic  fibers  in  the  liver,  kidneys,  in  the  lung, 
and  in  many  other  tissues.  In  bone-marrow  a  reticulum  is  found, 
in  the  meshes  of  which  are  the  cellular  elements  of  this  tissue. 


3.  FIBROUS  CONNECTIVE  TISSUE. 

Fibrous  connective  tissue  can  be  di\-ided  morphologically  into 
tivo  groups  :  In  one  the  bundles  of  fibers  cross  and  interlace  in 
all  directions,  forming  a  network  with  meshes  of  var>-ing  size — 
formless  or  areolar  connective  tissue.  In  the  other  the  bundles  of 
fibers  are  parallel  to  each  other,  as  in  tendon  and  many  of  the  apo- 
neuroses and  hgaments,  or  less  regularly  arranged,  yet  ver}-  densely 
woven,  as  in  fascias.  the  dura  mater,  and  the  firm,  fibrous  capsules 
of  some  of  the  organs. 

[a)  In  areolar  connective  tissue  the  bundles  of  white  fibers, 
w^hich  var}-  greatiy  in  size  and  which  often  divide  and  anastomose  with 
portions  of  other  branching  bundles,  intercross  and  interlace  in  all 
directions.  If  the  bundles  of  fibers  are  numerous,  the  interlacement  is 
more  compact,  thus  forming  a  dense  areolar  connective  tissue  ;  if  less 
numerous,  the  network  is  more  open,  as  in  loose  areolar  connective 
tissue.  Elastic  fibers  are  always  found  in  areolar  connective  tissue, 
though  in  var\-ing  quantit}-.  They  anastomose  to  form  a  network 
with  large,  irregular  meshes,  and  run  on  or  between  the  bundles  of 
white  fibers.      The  meshes  bet\veen  the  bundles  of  fibers,  and  the 


I02 


THE    TISSUES. 


minute  spaces  between  the  fibrils  in  these  bundles,  are  occupied  by 
a  semifluid,  homogeneous  substance  known  as  the  ground-substance , 
or  matrix.     The  fibrous  elements  of  areolar  connective  tissue  are, 


^ 

• 

'(^ 

- 

^ 

© 

~^ 

f 

ii- 

-    e                       ^" 

^_     ) 

c 

, 

'5^ 

6^ 

&, 

r 

^ 

isa 

S."^ 

- 

<£S 

@ 

- 

@. 

®  ^, 

-  "-       cj  ©         a'cT 

C7 

r 

^^ 

L^ 

'^®   ®'   Q 

Reticulum. 


Nucleus  of 
connec- 
tive-tis- 
sue cell. 


Blood- 
vessel. 


Fig.  64. — Reticular  connective  tissue  from  lymph-gland  of  man  ;  X  280.     Brush 

preparation. 

therefore,  imbedded  in  this  ground-substance.  In  dense  are- 
olar connective  tissue  the  fibrous  elements  appear  to  have 
nearly  displaced  the  ground-substance.  In  the  ground-substance 
are  found  irregular,  branched  spaces, — cell-spaces, — in  which 
lie  the  cellular  elements  of  this  connective  tissue.  These  spaces 
anastomose   by   means   of  their  branches,   thus  forming  part  of  a 

system  of  spaces  and  small  chan- 

^^     _  „-^^t  nels,  known  as  the  lymph  canal- 

-,^-   -  -  icular  system.    These  spaces  and 

.5==:—      '■(&     '       ,  -'  channels  permeate  the  ground- 

-"%;■ !%       substance  in  all  directions,  and 
^.rr~';^~    '  '-        serve   to   convey  lymph  to    the 

tissue  elements.    The  cell-spaces 
and  their  anastomosing  branches 
can  be  demonstrated  by  immers- 
ing    areolar     connective    tissue 
(preferably  from  a  young  animal), 
spread  out  in  a  thin  layer,  in  a 
solution   of  silver    nitrate  (i^) 
until  the  tissue  becomes  opaque. 
If  then  the  tissue  is  exposed  to 
sunlight,  the  silver  is  reduced  in  the  ground-substance,  giving  it  a 
brown  color,  while  the  cell-spaces  remain  unstained.     The  ground- 
substance  of  areolar  connective  tissue  contains  mucin. 


vv;- 


Fig.  65. — Areolar  connective  tissue 
from  the  subcutaneous  tissue  of  a  rat. 
Elastic  fibers  not  shown. 


THE    CONNECTIVE    TISSUES. 


103 


The   cellular   elements  of  areolar  connective  tissue,  which,  as 
above   stated,  are  found    in   the    cell-spaces,    are    either  fixed  con- 


Fig.    66. — Cell  -  spaces   in    the    ground-  Fig.  67. — Three  connective-tissue 

substance   of    areolar   connective   tissue    (sub-  cells  from  the  pia  mater  of  a  dog.  Stained 

cutaneous)  of  a  young  rat.     Stained  in  silver  in  methylene-blue  (intra  vitani). 
nitrate. 

nective -tissue  cells  or  wandering  or  migratory  cells.  The  former 
are  again  divided,  according  to  their  shape  and  structure,  into 
true  connective-tissue  cells  or  corpuscles,  plasma  cells,  mast-cells, 
and  pigment-cells. 

The  connective-tissue  cells  or  corpuscles  are  flattened,  variously 
shaped  cells  of  irregular  form,  usually  having  many  branches.  The 
protoplasm  is  free  from  granules  ;  the  nucleus,  situated  in  the  thicker 
portion  of  the  cell-body  and  of  oval  shape,  shows  a  nuclear  net- 
work and  one  or  several  nucleoli.     The  cells  assume  the  shape  of 


^1 

i 
/ 


\ 


'0 


Fig.  68.  — Two  pigment  cells  found  on  the  capsule  of  a  sympathetic  ganglion  of  a  frog. 


the  space  that  they  occupy  and  nearly  fill.  The  branches  of  neigh- 
boring cells  often  anastomose  through  the  fine  channels  uniting  the 
cell-spaces. 


I04 


THE    TISSUES. 


Protoplasm 


Plasma  cells  (Unna)  vary  in  size  and  shape  according  to  the 
space  which  they  occupy.  They  may  be  round,  oval,  or  spindle- 
shaped,  and  measure  from  6  a«  to  lo  /j.  The  nucleus  is  round  or 
oval.  They  are  characterized  by  the  fact  that  their  protoplasm 
stains  intensely  in  basic  aniline  dyes,  often  of  a  color  differing  from 

that  of  the  solution  used.  Accord- 
ing to  some  observers,  the  plasma 
cells  are  thought  to  be  developed 
from  the  connective-tissue  cells, 
while  others  regard  them  as  de- 
rived from  the  white  blood-cells 
(lymphocytes).  They  are  found  w. 
various  mucous  membranes  and  in 
lymphoid  tissues  generally. 

Mast-cells  (Ehrlich)  are  rela- 
tively large  cells  of  round,  oval,  or 
irregular  shape,  the  protoplasm  of 
which  contains  relatively  large 
granules  which  stain  chiefly  in 
basic  aniline  dyes,  which  granules 
are  often  found  in  such  numbers 
that  they  cover  up  the  nucleus. 
The  granules  are  stained  by  a 
number  of  basic  aniline  dyes,  often 
of  a  color  differing  from  that  of 
the  stain  used.  They  are  found  generally  in  mucous  membranes, 
generally  near  the  vessels,  in  the  skin,  in  involuntary  muscle,  and 
in  the  bone-marrow. 

Pigment  cells  are  branched  connective-tissue  cells,  in  the  proto- 
plasm of  which  are  found  brown  or  nearly  black  granules.  In  man 
they  occur  in  the  choroid  and  iris  and  in  the  dermis.  In  the  lower 
animals  they  have,  however,  a  much  wider  distribution,  and  in  the 
frog  and  other  amphibia  they  are  very  large  and  irregular.  These 
cells  have  the  power  of  withdrawing  their  processes  and,  to  a  limited 
degree,  of  changing  their  location  (dermis). 

The  wandering  or  migratory  cells  are  described  in  this  connec- 
tion not  because  they  form  one  of  the  structural  elements  of  areolar 
connective  tissue,  but  because  they  are  always  associated  with  it. 
They  are  lymph-  or  white  blood-cells,  which  have  left  the  lymph-  or 
blood-vessels  and  have  migrated  into  the  lymph  canalicular  system. 
They  possess  ameboid  movement,  and  wander  from  place  to  place, 
and  are  the  phagocytes  of  Metschnikoff.  They  seem  to  be  intrusted 
with  the  removal  of  substances  either  superfluous  or  detrimental  to 
the  body  (as  bacteria).  These  are  either  digested  or  rendered  harm- 
less. The  wandering  cells  even  transport  substances  thus  taken  up 
to  some  other  region  of  the  body,  where  they  are  deposited. 

In  the  peritoneum  and  other  serous  membranes  the  network 
formed  by  the  fibrous  tissue  lies  in  one  plane,  and  does  not  branch 


Fig.  69.  — Leucocyte  of  a  frog  with 
pseudopodia.  The  cell  has  included  a 
bacterium  which  is  in  process  of  diges- 
tion. (After  Metschnikoff,  from  O. 
Hertwig,  93,  II.) 


THE    CONNECTIVE    TISSUES.  IO5 

and  intercross  in  all  directions,  as  where  areolar  tissue  is  found  in 
larger  quantity.     (Fig.  70.) 

ip)  Tendons,  aponeuroses,  and  ligaments  represent  the  densest 
variety  of  fibrous  connective  tissue,  and  are  composed  almost 
wholly  of  white  fibrous  tissue.  This  is  found  in  the  form  of  rela- 
tively large  bundles  of  white  fibrils,  having  a  parallel  or  nearly 
parallel  course.  In  tendons  these  bundles  are  known  as  primary 
tendon  bundles  or  tendon  fasciculi.     The  fibrils  of  white  fibrous  con- 


Fibrils.    — -'jj^-- 


Nucleus. 


Fig.   70. — Fibrous  connective  tissue  (areolar)  from  the  great  omentum  of  the  rabbit; 

X400. 

nective  tissue  forming  the  fasciculi  are  cemented  together  by  an  in- 
terfibrillar  cement  substance.  Here  and  there  the  fasciculi  branch 
at  very  acute  angles  and  anastomose  with  other  fasciculi.  The  fas- 
ciculi are  grouped  into  larger  or  smaller  bundles,  the  secondary 
tendon  bundles,  which  are  surrounded  by  a  thin  layer  of  areolar  con- 
nective tissue,  and  in  part  covered  by  endothelial  cells.  Between 
the  tendon  fasciculi  there  is  found  a  ground-substance,  interfascicu- 
lar gro2ind-substancc,  identical  with  the  ground-substance  in  areolar 
connective  tissue.  In  this  there  are  cell-spaces  occupied  by  the 
tendon  cells,  morphologically  similar  to  the  branched  cells  of  areolar 
connective  tissue.  The  tendon  cells  are  arranged  in  rows  between  the 
tendon  fasciculi.  They  have  an  irregular,  oblong  body,  containing 
a  nearly  round  or  oval  nucleus.  Two,  three,  or  even  more  wing- 
like processes  (lamellae)  come  from  the  cell-body  and  pass  between 
the  tendon  fasciculi.  In  cross-section  the  tendon  cells  have  a 
stellate  shape. 

The  secondary  tendon  bundles  are  grouped  to  form  the  tendon, 
and  the  whole  is  surrounded  and  held  together  by  a  layer  of  areolar 
connective  tissue,  called  the  peritendineum.  From  this,  septa  pass  in 
between  the  secondary  tendon  bundles,  forming  the  internal  peri- 
tendineum. The  blood-  and  lymph-vessels  and  the  nerve-fibers 
reach  the  interior  of  the  tendon  through  the  external  and  internal 
peritendineum. 


io6 


THE    TISSUES. 


The  structure  of  an  aponeurosis  and  a  ligament  is  like  that  of  a 
tendon. 

The  structure  of  a  fascia,  the  dura  mater,  and  the  more  fully 


/  .    ,v 


Tendon  cell. 


„ Tendon  fibers. 


""  Tendon 
fasciculus. 


Fig.  71. — Longitudinal  section  of  tendon  ;       Fig.    72 — Cross-section   of   secondary 
X  270.  tendon  bundle  from  tail  of  a  rat. 

developed  gland  capsules,  differs  from  that  of  the  formed  connective 
tissues  above  described,  in  that  the  fasciculi  are  not  so  regularly- 
arranged,  but  branch  and  anastomose  and  intercross  in  several 
planes. 

(c)  Elastic  Fibrous  Tissue. — In  certain  connective  tissues  the 
elastic  fibers  predominate  greatly  over  the  fibers  of  white  fibrous 
connective  tissue.  These  are  spoken  of  as  elastic  fibrous  tissues  and 
their  structural  pecuHarities  warrant  the  making  of  a  special  sub- 
group. 

The  ligamentum  nuchae  of  the  ox  consists  almost  exclu- 
sively of  elastic  fibers,  many  of  which  attain  a  size  of  about  10//. 
The  elastic  fibers  branch  and  anastomose,  retaining,  however,  a 
generally  parallel  course.  They  are  separated  by  a  small  amount  of 
areolar  connective  tissue,  in  which  a  connective-tissue  cell  is  here 
and  there  found,  and  are  grouped  into  bundles  surrounded  by  thin 
layers  of  areolar  connective  tissue  ;  the  whole  ligament  receives  an 
investment  of  this  tissue.  In  cross-sections  of  the  ligamentum 
nuchae,  the  larger  elastic  fibers  have  an  angular  outline  ;  the  smaller 
ones  are  more  regularly  round  or  oval.  (Fig.  74.)  In  man  the 
ligamenta  subflava,  between  the  laminae  of  adjacent  vertebrae,  are 
elastic  ligaments. 

In  certain  structures  (arteries  and  veins),  the  elastic  tissue  is 
arranged  in  the  form  of  membranes.      It  is   generally  stated  that 


THE    CONNECTIVE    TISSUES. 


107 


such  membranes  are  composed  of  flat,  ribbon-like  fibers  or  bands  of 
elastic  tissue  arranged  in  the  form  of  a  network,  with  larger  or  smaller 
openings  ;  thus  the  term  fenestrated  membranes.  F.  P.  Mall  has 
reached  the  conclusion  that  such  membranes  are  composed  of  three 
layers — an  upper  and  a  lower  thin  transparent  layer  in  which  no 
openings  are  found  and  which  are  identical  with  the  sheaths  of 
elastic  fibers  described  by  this  observer,  and  a  central  layer,  contain- 
ing openings,  and  staining  deeply  in  magenta.  This  substance  is 
identical  with  the  central  substance  of  elastic  fibers. 


Areolar  con- 
nective tis- 
sue. 

Nucleus  of  con- 
nective-tissue 
cell. 


Fig.  73. — Tendon  cells  from  the 
tail  of  a  rat.  Stained  in  methylene- 
blue  [intra  vitam). 


Fig.  74. —  Cross-section    of    ligamentum 
nuchae  of  ox. 


4.  ADIPOSE  TISSUE. 

In  certain  well-defined  regions  of  the  body  occur  typical  groups 
of  fixed  connective-tissue  cells  which  always  change  into  fat-cells  (fat 
organs,Toldt).  Connective -tissue  cells  in  various  other  portions  of  the 
body  may  also  change  into  fat-cells,  but  in.  this  case  the  fat,  as  such, 
sometimes  disappears,  allowing  the  cells  to  resume  their  original  con- 
nective-tissue type,  only  again  to  appear  and  a  second  time  change  the 
character  of  the  tissue.  The  formation  of  fat  is  very  gradual.  Very 
fine  fat  globules  are  deposited  in  the  cell ;  these  coalesce  to  form 
larger  ones,  until  finally  the  cell  is  almost  entirely  filled  with  a 
large  globule  {yid.  also  H.  Rabl,  96). 
As  the  fat  globule  grows  larger  and 
larger,  the  protoplasm  of  the  cell,  to- 
gether with  its  nucleus,  is  crowded  to 
the  periphery.  The  protoplasm  then 
appears  as  a  thin  layer  just  within  the 
clear  cellular  membrane.  The  nucleus 
becomes  flattened  by  pressure,  until 
in  profile  view  it  has  the  appearance 

of  a  long,  flat  body.  In  regions  in  which  large  masses  of  fat- 
cells  are  developed,  they  are  seen  to  be  gathered  into  rounded 
groups  of  various  sizes  (fat  lobules)  separated  by  strands  of  con- 
nective tissue.  Such  lobules  have,  as  was  first  pointed  out  by 
Toldt,  a  typical  and  very  rich  blood-supply  from  the  time  that  they 
are   recognized    as    fat    organs    in    the    embryo.      A    small    artery 


•  Fat  drop. 
Cell-membrane. 


Fig-    75 — Scheme  of  a  fat-cell. 


io8 


THE    TISSUES. 


courses  through  the  center  of  the  fat  lobule,  breaking  up  into 
capillaries  which  form  a  network  around  the  fat  cells.  The  capil- 
laries unite  to  form  several  veins  which  are  situated  at  the  periphery 
of  the  lobule.  Where  fat  cells  develop  from  connective-tissue 
cells,  even  though  these  are  present  in  considerable  number  this 
typic  arrangement  of  the  blood-vessels  is  wanting. 

Microscopically,  fat  is  easily  recognized  by  its  peculiar  glistening 
appearance  (by  direct  light).  It  has  a  specific  reaction  to  certain 
reagents.  It  becomes  black  on  treatment  with  osmic  acid,  and  is 
stained  red  by  Sudan  III  and  blue  in  cyanin. 

5.  CARTILAGE. 

Cartilage  is  readily  distinguished  from  other  connective  tissues 
by  its  ground-substance  or  matrix, — intercellular  substance, — 
which  yields  chondrin  on  boiling.  Three  varieties  are  found  in 
higher  vertebrates:  (i)  hyaline  cartilage;  (2)  elastic  cartilage;  (3) 
white  fibro-cartilage  or  connective-tissue  cartilage. 

The  simplest  type  is  hyaline  cartilage,  so  named  because  of  its 


Matrix 


Cartilage  cell 


Fig.  76. — Hyaline  cartilage  (costal  cartilage  of  the  ox").  Alcohol  preparation  ; 
X  300.  The  cells  are  seen  inclosed  in  their  capsules.  In  the  figure  a  are  represented 
frequent  but  by  no  means  characteristic  radiate  structures. 


homogeneous  and  transparent  ground-substance,  which,  however, 
in  reality  consists  of  fibrils  and  an  interfibrillar  substance,  the  two 
having  essentially  the  same  refractive  index.  In  this  ground- 
substance  are  found  the  cartilage  cells,  occupying  spaces  known  as 
lacunae.  The  spaces  or  lacunae  are  surrounded  by  a  narrow  zone 
of  ground-substance,  which   does   not   stain  as   does  the   ground- 


THE    CONNECTIVE    TISSUES.  IO9 

substance  and  which  refracts  the  Hght  more  strongly.  This  zone  is 
generally  known  as  the  capsule  of  the  cartilage  cells.  As  pre- 
viously stated,  the  matrix  or  ground-substance,  develops  in  the 
exoplasm  of  the  protoplasmic  syncytium  from  which  cartilage  has 
its  origin,  while  the  endoplasm  and  nuclei  form  the  cartilage  cells. 
Cartilage  cells,  as  such,  are  of  various  shapes,  and  have  no  typical 
appearance.  They  are  usually  scattered  irregularly  throughout  the 
matrix,  but  are  often  arranged  in  groups  of  two,  three,  four,  or  even 
more  cells.  At  the  periphery  of  cartilage,  either  where  it  borders 
upon  a  cavity  (articular  cavit>^)  or  where  it  joins  the  perichondrium, 
the  cells  are  arranged  in  several  rows  parallel  to  the  surface  of  the 
tissue.  Cartilage  cells  often  contain  glycogen,  either  in  the  form 
of  drops  or  diffused  throughout  their  protoplasm. 

Cartilage  grows  by  intussusception,  and  an  appositional  growth, 
although  in  a  lesser  degree,  also  takes  place.  It  occurs  where  the 
cartilage  borders  upon  its  connective-tissue  sheath  ox  pcrichondrimn. 


Fig.  77. — From  a  section  through  the  cranial  cartilage  of  a  squid  (after  M.  Fiirbringer, 

from  Bergh). 

a  vascular,  fibrous-tissue  membrane  composed  of  white  and  elastic 
fibers,  which  covers  the  cartilage  except  where  it  forms  a  joint  sur- 
face. The  relations  of  the  cartilage  and  perichondrium  are  extremely 
intimate.  Fibers  are  seen  passing  from  the  perichondrium  into  the 
cartilaginous  matrix,  and  the  connective-tissue  cells  appear  to  change 
directly  into  cartilage-cells. 

Certain  observers  (Wolters.  Spronk,  and  others)  have  described  a 
system  ofcanaliculi  in  the  ground  substance,  which  are  said  to  unite 
the  lacunae  and  are  thought  to  serve  as  channels  for  the  passage  of 
lymph.  Such  structures  are,  however,  not  generally  recognized.  It 
is  an  interesting  fact,  however,  that  the  cartilage  of  certain  inverte- 
brate animals,  the  cephalopoda,  shows  cells  with  anastomosing  pro- 
cesses. (Fig.  jy^j  In  this  case  the  cartilage-cell  is  simjlar  to  a 
bone-cell,  thus  theoretically  allowing  of  the  possibility  of  the  meta- 
morphosis of  the  elements  of  cartilage  into  those  of  bone  (M.  Fiir- 
bringer). 


no 


THE    TISSUES. 


Hyaline  cartilage  occurs   as  articular  cartilage,   covering  joint 
surfaces,  as   costal   cartilage  and  in  the  nose,  larynx,  trachea,  and 


White  fibrous  connec- 
tive tissue. 


■  White  fibrocartilage. 


Insertion  of  liga- 
mentum  teres. 


►Hyaline  cartilage 


Fig.  78. — Insertion  of  the  ligamentum  teres  into  the  head  of  the  femur.     Longitudinal 

section ;  X  ^5°- 

bronchi.  All  bones  except  those  of  the  vault  of  the  skull  and  the 
majority  of  the  bones  of  the  face  are  preformed  in  hyaline  cartilage. 

In  white  fibrocartilage  (Fig.  'jZ)  there  are  from  the  beginning, 
even  in  precartilage,  fibrous  strands  in  the  ground-substance.  They 
preponderate  over  the  matrix  and,  as  a  rule,  have  a  parallel  direc- 
tion. White  fibrocartilage  is  found  in  the  intervertebral  and  inter- 
articular  disks,  the  symphysis  pubis,  and  in  the  insertion  of  the 
ligamentum  teres  ;  it  deepens  the  cavity  of  ball-and-socket  joints, 
and  lines  the  tendon  grooves. 

In  some  places  elastic  fibers  are  found  imbedded  in  hyaline  car- 
tilage— fibro-elastic  cartilage.  The  elastic  fibers  send  off  at  acute 
angles  finer  or  coarser  threads  which  interlace  to  form  a  delicate  or 


THE    CONNECTIVE    TISSUES. 


Ill 


dense  network  which  permeates  the  hyaHne  matrix  (Fig.  79),  pass- 
ing over  into  the  corresponding  elements  of  the  perichondrium. 
Elastic  cartilage  is  found  in  the  external  ear,  the  cartilage  of  the 
Eustachian  tube,  the  epiglottis,  a  portion  of  the  arytenoid  cartilages, 
and  the  cartilages  of  Wrisberg  and  Santorini. 


l~^-  Cartilage-cell. 


Fig.  79._Elastic  cartilage  from  the   external  ear  of  man;   X  76o.     a,  Fine  elastic 
network  in  the  immediate  neighborhood  of  a  capsule. 


The  ground-substance  of  cartilage  undergoes  changes  as  age 
advances.  In  certain  cartilages  there  is  observed  a  fibrillar  forma- 
tion, in  the  ground-substance  between  the  cells.  The  fibers  are 
coarse  and  differ  from  white  fibrous  or  yellow  elastic  fibers.  This 
change  is  observed  in  laryngeal  cartilages  as  early  as  the  twentieth 
year,  and  is  sometimes  designated  as  an  asbestos-like  alteration  of 
cartilage.  Calcification  occurs  in  many  cartilages— laryngeal, 
tracheal,  costal — and  consists  of  the  deposition  in  the  ground-sub- 
stance of  fine  granules  of  carbonate  of  lime,  first  in  the  immediate 
vicinity  of  the  cartilage  cells.  Calcification  is  observed  as  early  as 
the  twentieth  year  in  the  laryngeal  cartilages.  Ossification  may  be 
regarded  as  a  normal  occurrence  in  many  cartilages.  It  begins 
with  an  ingrowth  of  blood-vessels  from  the  perichondrium  into  the 
matrix.  These  vessels  are  surrounded  by  connective  tissue.  Around 
such  locations  ossification  occurs.  Chievitz  has  shown  that  the 
laryngeal  cartilages  begin  to  ossify  in  men  at  about  the  twentieth 
year,  and  in   women   at  about  the  thirtieth  year;  and  the  tracheal 


112  THE    TISSUES. 

cartilage  in  men  about  the  fortieth  year,  and  in   women  about  the 
sixtieth  year. 

To  obtain  chondrin,  a  piece  of  cartilage  matrix  is  placed  in  a 
tube  containing  water.  This  is  hermetically  closed  and  heated  to 
120°  C,  after  which  it  is  opened  and  the  fluid  filtered  and  treated 
with  alcohol.  A  precipitate  of  chondrin  is  the  result.  This  sub- 
stance is  insoluble  in  cold  water,  alcohol,  and  ether,  but  soluble  in 
hot  water,  although,  on  cooling,  it  gelatinizes.  In  contrast  to  gel- 
atin, chondrin  is  precipitated  by  acetic  acid.  This  precipitate  does 
not  redissolve  in  an  excess  of  this  acid  but  disappears  in  an  excess 
of  certain  mineral  acids. 


6.  BONE. 

{a)  Structure  of  Bone. — Bone  nearly  always  develops  from  a 
connective-tissue  foundation,  even  where  it  occurs  in  places  formerly 
occupied  by  cartilage. 

The  inorganic  substance  of  bone  is  deposited  in  or  between  the 
fibers  of  connective  tissue,  while  the  cells  of  the  latter  are  trans- 
formed into  bone-cells. 

As  in  connective  tissue,  so  also  in  bone,  the  ground-substance, 
is  fibrous.  Between  the  fibers  remain  uncalcified  cells,  bone-cells, 
each  of  which  rests  in  a  cavity  of  the  matrix — lacuna. 

Primarily,  bone  consists  of  a  single  thin  lamella,  its  later  com- 
plicated structure  being  produced  by  the  formation  of  new  lamellae 
in  apposition  to  the  first.  During  its  development  the  bone  becomes 
vascularized,  and  the  vessels  are  inclosed  in  especially  formed  canals 
known  as  vascular  or  Haversian  canals. 

The  bone-cells  have  processes  that  probably  anastomose,  and 
that  lie  in  special  canals  known  as  bone  canaliaili.  Whether,  in 
man,  all  the  processes  of  bone-cells  anastomose  is  still  an  open 
question. 

The  appearance  presented  by  a  transverse  section  of  the  shaft 
of  a  long  bone  is  as  follows  :  In  the  center  is  a  large  marrow  cavity, 
and  at  the  periphery  the  bone  is  covered  by  a  dense  connective- 
tissue  membrane,  the  periosteum.  In  the  new-born  and  iry  young  in- 
dividuals the  periosteum  is  composed  of  three  layers — an  outer  layer, 
consisting  mainly  of  rather  coarse,  white  fibrous-tissue  bundles  that 
blend  with  the  surrounding  connective  tissue  ;  a  middle  fibro-elastic 
layer,  in  which  the  elastic  tissue  greatly  predominates  ;  and  an  inner 
layer,  the  osteogenetic  layer,  vascular  and  rich  in  cellular  elements, 
containing  only  a  few  smaller  bundles  of  white  fibrous  tissue.  In 
the  adult  the  osteogenetic  layer  has  practically  disappeared,  leav- 
ing only  here  and  there  a  few  of  the  cells  of  the  layer,  while 
the  fibro-elastic  layer  is  correspondingly  thicker  (Schulz,  96).  A 
large  number  of  Haversian  canals  containing  blood-vessels,  seen 
mostly  in  transverse  section,  are  found  in  compact  bone-substance. 


THE    CONNECTIVE    TISSUES. 


113 


Lamellje  of  bone  are  plainly  visible  throughout  the  ground-sub- 
stance, and  are  arranged  in  the  following  general  systems  : 

First,  there  is  a  set  of  bone  lamellae  running  parallel  to  the  ex- 
ternal surface  of  the  bone,  while  another  set  is  similarly  arranged 
around  the  marrow  cavity.  These  are  the  so-called  fundamental, 
or  outer  and  innet^  circumferential  lamellcB  (known  also  as  periosteal 
and  marrow  lamellce).  Around  the  Haversian  canals  are  the  con- 
centrically arranged  lamellae,  forming  systems  of  Haversian  or  con- 
centric lamellcB.  Besides  the  systems  already  mentioned,  there  are 
found  interstitial  ox  ground  lamellcB  wedged  in  between  the  Haversian 


Fig.  80. —  Longitudinal  section       Figs.  81  and  82. — Lamellse  seen  from  the  surface; 
through  a  lamellar  system.  X  4^0  (after  v.  Ebner  75). 

a,  Primitive   fibrils    and   fibril-bundles ;    c,  bone-corpuscles  with  bone-cells ;    J,  bone 

canaliculi. 


or  concentric  systems  of  lamellae.      Some  authors  group  the  inter- 
stitial lamellae  with  the  systems  of  fundamental  lamellae. 

Lying  scattered  between  the  lamellae  are  found  spaces  known  as 
bone  corpuscles  (Virchow)  or  laciince.  These  are  present  in  all  the 
lamellar  systems.  It  is  very  probable  that  all  the  |acunae  are  in 
more  or  less  direct  communication  with  each  other  by  means  of  fine 
canals  called  canaliculi  ( i .  i  //  to  i . 8  //  in  diameter).  It  can  be  demon- 
strated without  difficulty  that  the  lacunae  of  a  single  lamellar  sys- 
tem communicate  not  only  with  each  other,  but  also  with  those  of 
8 


114 


THE    TISSUES. 


adjacent  systems.  In  the  lamellae  adjoining  the  periosteum  and  mat- 
row  cavity  the  canaliculi  end  respectively  in  the  subperiosteal  tissue 
and  in  the  marrow  cavity.  The  canaliculi  of  the  Haversian  lamellae 
empty  into  the  Haversian  canals. 


>    Outer  circum- 
ferential 
lamellse. 


Haversian  or 

concentric 
lamellae. 


r          ■" 

"■    -^ 

'^^'Cu 

—  ""^    ^^ 

^  ^^  ^ 

O. : 

■»      ^ 

y  --  >  >     ^'  ^  * 


'<^^ 


/-■,  '.^^  .* 


t 


-Haversian 
canal. 


J     -*^Vi-'?'-^^* Interstitial 


^  S   Inner  circum- 


ferential 
lamellae. 


Fig,  83. — Segment  of  a  transversely  ground  section  from  the  shaft  of  a  long  bone,  show- 
ing all  the  lamellar  systems.     Metacarpus  of  man ;  X  5^- 


The  lamellae  of  bone  are  composed  of  fine  white  fibrous-tissue 
fibrils,  embedded  in  a  ground-substance,  in  which  they  are  arranged 
in  layers,  superimposed  in  such  a  way  that  the  fibrils  in  the  several 
layers  cross  at  about  a  right  angle,  forming  an  angle  of  45°  with 


THE    CONNECTIVE    TISSUES. 


115 


the  long  axis  of  the  Haversian  canal.  It  is  as  yet  undecided 
whether  the  mineral  salts  (phosphate  and  carbonate  of  lime,  sodium 
Chlorid,  magnesium  salts,  etc.)  are  deposited  in  the  ground-substance 
(v.  Ebner)  or  in  the  fibrillae  (Kölhker).  The  lacunae  {13/2  to  t,i  fx 
long,  6  fxto  1 5  n  wide,  and  4//  to  9  //  thick)  have,  in  common  with  the 
canaliculi,  walls  which  present  a  greater  resistance  to  the  action  of 
strong  acids  than  the  rest  of  the  solid  bone-substance.  In  each 
lacuna  there  is  found  a  bone-cell,  the  nucleated  body  of  which 
practically  fills  the  lacuna,  while  its  processes  extend  out  into  the 
canaliculi. 

The  Haversian  canals  contain  blood-vessels,  either  an  artery  or 
a  vein  or  both.  Between  the  vessels  and  the  walls  of  the  canals 
are  perivascular  spaces  bounded  by  endothelial  cells,  resting  on  the 
adventitious  coats  of  the  vessels  and  the  sides  of  the  canals.  Into 
these  spaces  empty  the  canaliculi  of  the  Haversian  system.  Lymph- 
spaces  beneath  the  periosteum  and  at  the  periphery  of  the  marrow 


Lacuna.  •* 

Canaliculi.  — 


Haversian  canal.  •■ 


Fig.  84. — Portion  of  a  transversely  ground  disc  from  the  shaft  of  a  human  femur; 

X400. 

cavity  communicate  directly  with  the  canaliculi  of  the  circumferen- 
tial systems. 

All  the  lacunae  and  canaliculi  should  be  thought  of  as  filled  by 
lymph  plasma  which  circulates  throughout,  bathing  the  bone-cells 
and  their  processes.  The  formed  elements  of  the  lymph  are  prob- 
ably too  large  to  force  their  way  through  the  very  small  canaliculi. 
The  plasma  current  probably  flows  from  the  periosteal  and  marrow 
regions  toward  the  Haversian  canals. 

Between  the  lamellae  are  bundles  of  fibers  (some  of  which  are 
calcified),  which  can  be  demonstrated  by  heating  the  bone,  or  in  de- 
calcified preparations  on  staining  by  certain  methods.  These  are  the 
so-called /^£V'.y  of  Sharper  ;  in  the  adult  they  contain  elastic  fibers. 

In  the  circumferential  lamellae  are  found  canals,  not  surrounded 
by  concentric  lamellae,  which  convey  blood-vessels  from  the  perios- 
teum to  the  Haversian  canals.      These  are  called  Volkniann's  canals. 

The  structure  of  bone-marrow  will  be  discussed  with  the  blood- 
forminp-  organs. 


Il6  THE    TISSUES. 

{b)  Development  of  Bone. — Nearly  all  the  bones  of  the  adult 
body  are,  in  the  earlier  stages  of  embryonic  life,  preformed  in  embry- 
onic cartilage.  As  development  proceeds,  this  embryonic  cartilage 
assumes  the  character  of  hyaline  cartilage,  its  cells  becoming  vesic- 
ular, and  probably  disappearing.  In  the  matrix,  however,  there 
are  formed  spaces  that  are  soon  occupied  by  cells  and  vessels  which 
grow  in  from  a  fibrous-tissue  membrane  (the  future  periosteum)  sur- 
rounding the  cartilage  fundaments  of  the  bones.  These  cells  deposit 
a  bone  matrix  in  the  cartilage  spaces.  Bone  developed  in  this  man- 
ner is  known  as  endochondral  or  intracartilaginoiis  bone.  In  certain 
bones — namely,  those  of  the  vault  of  the  skull  and  nearly  all  the 
bones  of  the  face — there  is  no  preformation  in  cartilage,  these  bones 
being  developed  from  a  connective -tissue  foundation.  They  are 
known  as  intramembranoKS  bones.  As  will  become  evident  upon 
further  discussion  of  the  subject,  the  formation  of  fibrous-tissue 
bone  (intramembranous)  is  not  confined  to  bones  not  preformed  in 
cartilage.  In  bones  preformed  in  cartilage,  fibrous-tissue  bone  de- 
velops from  the  connective -tissue  membrane  surrounding  the  carti- 
lage fundaments,  the  two  types  of  bone-development  going  on  simul- 
taneously in  such  bones.  Attention  may  further  be  drawn  to  the 
fact  that  nearly  all  endochondral  bone  is  absorbed,  so  that  the 
greater  portion  of  all  adult  bone,  even  that  preformed  in  cartilage, 
is  developed  from  a  foundation  of  fibrous  tissue.  The  two  modes 
of  ossification — endochondral  or  intracartilaginous  and  intramem- 
branous— even  though  appearing  simultaneously  in  the  majority  of 
bones,  will,  for  the  sake  of  clearness,  be  discussed  separately. 

I .  Endochondral  Bone=development. — The  cartilage  that  forms 
the  fundaments  of  the  bones  preformed  in  cartilage  has  at  first  the 
appearance  of  embryonic  cartilage,  consisting  largely  of  cells  with 
a  small  amount  of  intercellular  matrix.  These  fundaments  are  sur- 
rounded by  a  fibrocellular  membrane — the  perichondrium.  Ossifi- 
cation is  initiated  by  certain  structural  changes  in  the  embryonic 
cartilage,  in  one  or  several  circumscribed  areas,  known  as  centers  of 
ossification.  In  the  long  bones  a  center  of  ossification  appears  in  the 
middle  of  the  future  diaphysis.  In  this  region  the  intercellular 
matrix  increases  in  amount  and  the  cells  in  isize  ;  thus  the  embry- 
onic cartilage  assumes  the  character  of  hyaline  cartilage.  This  is 
followed  by  a  further  increase  in  the  size  of  the  cartilage-cells,  at 
the  expense  of  the  thinner  partitions  of  matrix  separating  neighbor- 
ing cells,  while  at  the  same  time  lime  granules  are  deposited  in  the 
matrix  remaining.  During  this  stage  the  cells  appear  first  vesicu- 
lar, distending  their  capsules,  then  shrunken,  only  partly  filling  the 
enlarged  lacunae.  They  stain  less  .deeply,  and  their  nuclei  show 
degenerative  changes.  The  center  of  ossification,  in  the  middle  of 
which  these  changes  are  most  pronounced,  is  surrounded  by  a  zone 
in  which  these  structural  changes  are  not  so  far  advanced  and  which 
has  the  appearance  at  its  periphery  of  hyaline  cartilage. 

Simultaneously  with  these  changes  in  the  cartilage,  a  thin  layef 


THE    CONNECTIVE    TISSUES. 


117 


of  bone  is  deposited  by  the  perichondrium  (in  a  manner  to  be 
described  under  the  head  of  intramembranous  bone-development) 
and  the  perichondrium  becomes  the  periosteum.  This  in  the  mean- 
time has  differentiated  into  two  layers — an  outer,  consisting  largely 
of  fibrous  tissue  with  few  cellular  elements,  and  an  inner,  the 
osteogenetic  layer,  vascular  and  rich  in  cellular  elements  and  con- 
taining few  fibrous-tissue  fibers. 

Ossification  in  the  cartilage  begins  after  the    above-described 


Vesicular  cartilage- 
cells. 


Primary  periosteal 
bone  lamella. 


Periosteal  bud. 


Periosteum. 


Unaltered  hyaline 
cartilage. 


Fig.  85. — Longitudinal  section  through  a  long  bone  (phalanx)  of  a  lizard  embryo. 
The  primary  bone  lamella  originating  from  the  periosteum  is  broken  through  by  the  peri- 
osteal bud.  Connected  with  the  bud  is  a  periosteal  blood-vessel  containing  red  blood- 
corpuscles. 


Structural  changes  have  taken  place  at  the  center  of  ossifica- 
tion. Its  commencement  is  marked  by  a  growing  into  the  cartilage 
of  one  or  several  buds  or  tufts  of  tissue  derived  principally  from 
the  osteogenetic  layer  of  the  periosteum.  As  the  periosteal  buds 
grow  into  the  cartilage,  some  of  the  septa  of  matrix  separating  the 
altered  cartilage-cells  disappear,  and  the  cells  become  free  and 
probably  degenerate.    In  this  way  the  cartilage  at  the  center  of  ossi- 


ii8 


THE    TISSUES. 


fication  becomes  hollowed  out,  and  there  are  formed  irregular  anas- 
tomosing spaces,  primary  marrow  spaces,  separated  by  partitions  or 
trabeculse  of  calcified  cartilage  matrix.  Into  these  primary  mar- 
row spaces  grow  the  periosteal  buds,  consisting  of  small  blood- 
vessels, cells,  and  some  few  connective-tissue  fibers,  forming  embry- 
onic marrow  tissue.     Some  of  the  cells  which  have  thus  grown  into 


Groove  of 
ossification, 


—     Periosteum, 


Periosteal  bone 

lamella. 
Primary  marrow 

spaces. 


Fig.  86. — Longitudinal  section  of  the  proximal  end  of  a  long  bone  (sheep  embryo)  ; 

X30- 

the  primary  marrow  spaces  arrange  themselves  in  layers  on  the 
trabeculse  of  calcified  matrix,  which  they  envelop  with  a  layer  of 
osseous  matrix  formed  by  them.  The  cells  thus  engaged  in  the 
formation  of  osseous  tissue  are  known  as  osteoblasts. 

Ossification  proceeds  from  the  center  of  ossification  toward  the 


THE    CONNECTIVE    TISSUES. 


119 


extremities  of  the  diaphysis  (in-  a  long  bone),  and  is  always  preceded 
as  at  the  center  of  ossification,  by  the  characteristic  structural 
changes  above  described.  Beginning  at  the  center  of  ossification  and 
proceeding  toward  either  extremity  of  the  diaphj^sis,  the  enlarged  and 
vesicular  cartilage-cells  will  be  observed  to  be  arranged  in  quite  reg- 
ular columns,  separated  by  septa  or  tra- 
beculae  of  calcified  cartilage  matrix.  The 
cells  thus  arranged  in  columns  show  the 
degenerative  changes  above  described. 
They  are  shrunken  and  flattened,  and 
their  nuclei,  when  seen,  stain  less  deeply 
than  the  nuclei  of  normal  cartilage-cells. 
Beyond  this  zone  of  columns  of  altered 
cartilage-cells  are  found  smaller  or  larger 
groups  of  less  changed  cartilage-cells, 
and  beyond  this  zone,  hyaline  cartilage. 

The  arrangement  of  the  cartilage- 
cells  in  the  columns  above  mentioned  is, 
according  to  Schiefferdecker,  mainly  due 
to  two  factors  —  the  current  of  lymph 
plasma  which  flows  from  the  center  of 
ossification  toward  the  two  extremities  of 
the  cartilage  fundament,  and  the  mutual 
pressure  exerted  by  the  groups  of  carti- 
lage-cells in  their  growth  and  prolifera- 
tion. Ossification  proceeds  from  the  cen- 
ter of  the  diaphysis  toward  its  two  ex- 
tremities by  a  growth  of  osteoblasts  and 
small  vessels  into  the  columns  of  carti- 
lage-cells. Here,  also,  these  degenerate, 
leaving  in  their  stead  irregular,  oblong, 
anastomosing  spaces,  separated  by  septa 
and  trabeculae  of  calcified  cartilage  ma- 
trix on  which  the  osteoblasts  arrange 
themselves  in  layers,  and  which  they 
envelop  in  osseous  tissue.  In  a  longi- 
tudinal section  of  a  long  bone,  preformed 
in  cartilage,  the  various  steps  of  endo- 
chondral bone-development  may,  there- 
fore, be  observed  by  viewing  the  prepa- 
ration from  either  end  to  the  center  of  the 
diaphysis,  as  may  be  seen  in  figures  86, 
87.  The  former  represents  the  appear- 
ance as  seen  under  low  magnification,  the  latter  a  small  portion  of 
such  a  section  from  the  area  of  ossification,  more  highly  magnified. 

Adjoining  the  primary  marrow  spaces  is  vesicular  cartilage 
and  columns  and  groups  of  cartilage-cells  and  finally  hyaline  car- 
tilage. 


Fig.  87. — Longitudinal  sec- 
tion through  area  of  ossification 
from  long  bone  of  human  em- 
bryo. 


.J20  THE    TISSUES. 

In  the  upper  portion  of  figure  87  is  observed  a  zone  composed 
of  groups  of  cartilage-cells,  adjoining  this  a  zone  composed  of 
columns  of  vesicular  and  shrunken  cartilage-cells,  the  nuclei  of  which 
are  indistinctly  seen.  These  columns  are  separated  by  septa  and 
trabeculae  of  calcified  matrix.  This  zone  is  followed  by  one  in 
which  the  cartilage-cells  have  disappeared,  leaving  spaces  into 
which  the  osteoblasts  and  small  blood-vessels  have  grown.  In  cer- 
tain parts  of  the  figure,  the  osteoblasts  are  arranged  in  a  layer  on 
the  trabeculae  of  calcified  cartilage,  some  of  which  are  enveloped 
in  a  layer  of  osseous  matrix,  less  deeply  shaded  than  the  darker  car- 
tilage remnants. 

As  the  development  of  endochondral  bone  proceeds  from  the 
center  of  ossification  toward  the  extremities  of  the  diaphysis  in  the 
manner  described,  the  primary  marrow  spaces  at  the  center  of  ossi- 
fication are  enlarged,  a  result  of  an  absorption  of  many  of  the  smaller 
osseous  trabeculae  and  the  remnants  of  calcified  cartilage  matrix 
enclosed  by  them.  In  this  process  are  concerned  certain  large 
and,  for  the  most  part,  polynuclear  cells,  which  are  differentiated 
from  the  embryonic  marrow.  These  are  the  osteoclasts  (bone  break- 
ers) of  Kölliker  (73).  They  are  43  //  to  91  //  long  and  30  fi  to  40  ft 
broad,  and  have  the  function  of  absorbing  the  bone.  The  spaces 
which  they  hollow  out  during  the  beginning  of  the  process  appear 
as  small  cavities  or  indentations,  containing  osteoclasts  either  single 
or  in  groups,  and  are  known  as  Howshifs  lacuiKE.  All  bone 
absorption  goes  hand  in  hand  with  their  appearance.  At  the  same 
time,  the  osseous  trabeculae  not  absorbed  become  thickened  by  a 
deposition  of  new  layers  of  osseous  tissue  (by  osteoblasts),  during 
which  process  some  of  the  osteoblasts  are  enclosed  in  the  newly 
formed  bone  and  are  thus  converted  into  bone-cells.  In  this  way 
there  is  formed  at  the  center  of  ossification  a  primary  or  embryonic 
spongy  or  cancellous  bone,  swxxo\xx\^\Vig  secondary  vtarrow  spaces  or 
Haversian  spaces,  filled  with  embryonic  marrow.  This  process  of 
the  formation  of  embryonic  cancellous  bone  follows  the  primary 
ossification  from  the  center  of  ossification  toward  the  extremities  of 
the  diaphysis.  It  should  be  further  stated,  that  long  before  the 
developing  bone  has  attained  its  full  size — indeed,  before  the  end  of 
embryonic  life — the  embryonic  cancellous  bone  is  also  absorbed 
through  the  agency  of  osteoclasts.  The  Haversian  spaces  are  thus 
converted  into  one  large  cavity,  which  forms  a  portion  of  the  future 
marrow  cavity  of  the  shaft  of  the  fully  developed  bone.  The 
absorption  of  the  embryonic  cancellous  bone  begins  at  the  center 
of  ossification  and  extends  toward  the  ends  of  the  diaphysis. 

Some  time  after  the  beginning  of  the  process  of  bone  develop- 
ment at  the  center  of  ossification  of  the  diaphysis,  centers  of 
ossification  appear  in  the  epiphyses,  the  manner  of  the  develop- 
ment of  bone  being  here  the  same  as  in  the  diaphysis.  Several 
periosteal  buds  grow  into  each  center  of  ossification,  filling  the 
irregular  spaces  formed  by   the    breaking   down    of  the   degener- 


THE    CONNECTIVE    TISSUES.  121 

ated  cartilage-cells.  Osteoblasts  are  arranged  in  rows  on  the 
trabeculse  of  cartilage  thus  formed,  which  they  envelop  in  osseous 
tissue.  As  development  proceeds,  the  primary  osseous  tissue  is 
converted  into  embryonic  cancellous  bone  as  above  described. 

In  the  development  of  the  epiphyses,  as  in  the  development  of 
the  smaller  irregular  bones,  the  formation  of  bone  proceeds  from 
the  center  or  centers  of  ossification  in  all  directions,  and  not  only 
in  a  direction  parallel  to  the  long  axis  of  the  bone  as  described  for 
the  diaphysis.  The  epiphyses  grow,  therefore,  in  thickness  as  well 
as  in  length,  by  endochondral  bone-development. 

There  remains  between  the  osseous  tissue  developed  in  the  dia- 
physis and  that  in  the  epiphyses,  at  each  end  of  the  diaphysis,  a  zone 
of  hyaHne  cartilage  in  which  ossification  is  for  a  long  time  delayed  ; 
this  is  to  permit  the  longitudinal  growth  of  the  bone.  These  layers  of 
cartilage  constitute  the  epiphyseal  cartilages.  Here  the  periosteum 
(perichondrium)  is  thickened  and  forms  a  raised  ring  around  the 
cartilage.  As  it  penetrates  some  distance  into  the  substance  of  the 
cartilage,  the  latter  is  correspondingly  indented.  (Fig.  86.)  The  im- 
pression thus  formed  appears  in  a  longitudinal  section  of  the  bone 
as  an  indentation, — the  ossification  groove  {encoche  d' ossification, 
Ranvier,  89).  That  portion  of  the  perichondrium  filling  the  latter 
is  called  the  ossification  7'idge.  The  relation  of  the  elements  of  the 
perichondrium  to  the  cartilage  in  the  region  of  the  groove  just 
described  is  an  extremely  intimate  one,  both  tissues,  perichondrium 
and  cartilage,  merging  into  each  other  almost  imperceptibly.  It  is 
a  generally  accepted  theory  that  so  long  as  the  longitudinal  growth 
of  the  bone  persists,  new  cartilage  is  constantly  formed  at  these 
points  by  the  perichondrium.  In  the  further  production  of  bone 
this  newly  developed  cartilage  passes  through  the  preliminary 
changes  necessary  before  the  actual  commencement  of  ossification 
— /.  e.,  it  goes  through  the  stages  of  vesicular  cartilage  and  the 
formation  of  columns  of  cartilage-cells,  in  place  of  which,  later,  the 
osteoblasts  and  primary  marrow  cavities  develop. 

By  the  development  of  new  cartilage  elements  from  the  encoche 
the  longitudinal  growth  of  the  bone  is  made  possible ;  at  the  same 
time,  those  portions  of  the  cartilage  thus  used  up  in  the  process  of 
ossification  are  immediately  replaced.      (Fig.  88.) 

The  following  brief  summary  of  the  several  stages  of  endochon- 
dral bone-development  may  be  of  service  to  the  student  : 

1.  The  embryonic  cartilage  develops  into  hyaline  cartilage, 
beginning  at  the  centers  of  ossification. 

2.  The  cartilage-cells  enlarge  and  become  vesicular.  In  the 
diaphysis  of  long  bones  such  cells  are  arranged  in  quite  regular 
columns,  while  in  the  epiphyses  and  irregular  bones  this  arrange- 
ment is  not  so  apparent. 

3.  Calcification  of  the  matrix  ensues  ;  the  cartilage-cells  disap- 
pear (degenerate)  ;  primary  marrow  spaces  develop. 

4.  Ingrowth  of  periosteal  buds.     The  osteoblasts  are  arranged 


122 


THE    TISSUES. 


in  layers  on  the  trabeculae  of  calcified  cartilage,  which  they  envelop 
with  osseous  tissue. 

5.  Osteoclasts  cause  the  absorption  of  many  of  the  smaller 
osseous  trabeculae  ;  others  become  thickened  by  a  deposition  of 
new  layers  of  osseous  tissue.  Osteoblasts  are  enclosed  in  bone- 
tissue  and  become  bone-cells.  In  this  way  there  is  formed  embry- 
onic cancellous  bone,  bounding  Haversian  spaces  inclosing  embry- 
onic marrow. 

6.  In  the  diaphysis,  the  greater  portion  of  the  embryonic  can- 
cellous bone  is  also  absorbed  (by  osteoclasts)  ;  the  Haversian  spaces 
unite  to  form  a  part  of  the  marrow  space  of  the  shaft  of  the  bone. 

2.  Intramembranous  Bone. — This,  the  simpler  type  of  ossifi- 
cation, occurs  in  bone  developed  from  a  connective-tissue  founda- 
tion, and   is    exemplified   in    the    formation    of  the    bones    of  the 


^_ Blood- 

"^  vessel. 


ridge.         .  #^f^      "^ 
Epiphyseal    K^ 
cartilage. — ^ 


Fig.  88.  — Longitudinal  section  through  epiphysis  of  arm  bone  of  sheep  embryo  ;   X  ^  2. 
a,  b.  Primary  marrow  spaces  and  bone  lamellse  of  the  diaphysis. 


cranial  vault  and  the  greater  number  of  the  bones  of  the  face,  and 
also  in  bone  developed  from  the  periosteum  (perichondrium)  sur- 
rounding the  cartilage  fundaments  of  endochondral  bone.  All 
fibrous-tissue  bone  is  developed  in  the  same  way. 

The  intramembranous  bone-development  begins  by  an  approxi- 
mation and  more  regular  arrangement  of  the  osteoblasts  of  the 
osteogenetic  layer  of  the  periosteum  about  small  fibrous-tissue 
bundles.  The  osteoblasts  then  become  engaged  in  the  formation 
of  the  osseous  tissue  which  envelops  the  fibrous-tissue  bundles. 
In  this  way  a  spongy  bone  with  large  meshes  is  formed,  consisting 
of  irregular  osseous  trabeculae,  surrounding  primary  marrow  spaces. 
These  latter  are  filled  by  embryonic  marrow  and  blood-vessels  de- 
veloped from  the  tissue  elements  of  the  periosteum  not  engaged  in 
the  formation  of  bone. 


THE    CONNECTIVE    TISSUES. 


123 


Intramembranous  bone  first  appears  in  the  form  of  a  thin  lamella 
of  bone,  which  increases  in  size  and  thickness  by  the  formation  of 
trabeculae  about  the  edges  and  surfaces  of  that  previously  formed 
and  in  the  manner  above  described.  A  layer  of  intramembranous 
bone  thus  surrounds  the  endochondral  bone  in  bones  preformed  in 
hyaline  cartilage.  The  two  modes  of  ossification  may,  therefore, 
be  observed  in  either  a  cross  or  a  longitudinal  section  of  a  develop- 
ing bone  preformed  in  hyaline  cartilage.  In  such  preparations 
the  endochondral  bone  can  be  readily  distinguished  from  the  intra- 


--6, (0, -Primary 

*'  marrow 


Fig.  89. — Section  through  the  lower  jaw  of  an  embryo  sheep  (decalcified  with  picric 
acid)  ;  >(  S^O-  -^^  '^  ^'^d  immediately  below  are  seen  the  fibers  of  a  primitive  marrow 
cavity  lying  close  together  and  engaged  in  the  formation  of  the  gromid-substance  of  the 
bone,  while  the  cells  of  the  marrow  cavity,  with  their  processes,  arrange  themselves  on 
either  side  of  the  newly  formed  lamella  and  functionate  as  osteoblasts. 


membranous  bone  by  reason  of  the  fact  that  remnants  of  calcified 
cartilage  matrix  may  be  observed  in  the  osseous  trabeculae  of  the 
former.  It  will  be  remembered  that  these  osseous  trabeculae  de- 
velop about  the  calcified  cartilage  matrix  remaining  after  the  dis- 
appearance of  the  cartilage-cells.  In  figure  90,  which  shows  a 
cross-section  of  a  bone  from  the  leg  of  a  human  embryo,  these  facts 
are  clearly  shown.  A  study  of  this  figure  shows  the  endochondral 
bone,    with   the   remnants    of  the    cartilage    matrix  (shaded  more 


124  THE    TISSUES. 

deeply)  inclosed  in  osseous  tissue,  making  up  the  greater  portion 
of  the  section  and  surrounded  by  the  intramembranous  bone. 

In  figure  91,  more  highly  magnified,  the  relations  of  endochon- 
dral to  intramembranous  bone  and  the  details  of  their  mode  of 
development  are  shown  ;  also  the  structure  of  the  periosteum. 

As  was  stated  in  the  previous  section,  soon  after  the  formation 
of  the  endochondral  bone,  this  is  again  absorbed  ;  the  process  of 
endochondral  bone-formation  and  absorption  extending  from  the 
center  of  ossification  toward  the  ends  of  the  diaphysis.  Before  the 
absorption  of  the  endochondral  bone,  the  intramembranous  bone 
has  attained  an  appreciable  thickness  and  surrounds  the  marrow 
cavity  formed  on  the  absorption  of  the  endochondral  bone.    Before, 


/. 


Hi 

iM 

7'--^-'{:-i^.    -'::i?:'^^ 

'''■'^'.  -■■':'■ 

^"  '^M:;Wi'-:^^M  \ 

r;;"',\};i; 

;'->.V:  ■■,-;■ 

.:■■:•>  ■'■•K^Slili'  \ 

';-x..;::  ,■'■",;; 

;  '•'■'':  ■■'■'■'■' 

■">'^.-;V  "•■:->'. 

■  y^'-^^'V.  ■■.i'^^^'-^y-.y-''^-  •  ,'?¥; 

''y]y^^:i^ 

iSilS%--i'l:'''|i   i 

Fig.  90. — Cross-section  of  developing  bone  from  leg  of  human  embryo,  showing  endo- 
chondral and  intramembranous  bone-development. 

however,  the  marrow  cavity  can  attain  its  full  dimensions,  much  of 
the  intramembranous  bone  must  also  undergo  absorption.  While 
intramembranous  bone  is  being  developed  from  the  periosteum  and 
thus  added  to  the  outer  surface  of  that  already  formed,  osteoclasts 
are  constantly  engaged  in  its  removal  from  the  inner  surface  of  the 
intramembranous  bone.  The  marrow  cavity  is  thus  enlarged,  the 
process  continuing  until  the  shaft  attains  its  full  size. 

The  compact  bone  of  the  shaft  is  developed  from  the  primary 
spongy  intramembranous  bone  after  the  following  manner  :  The 
primary  marrow  spaces  are  enlarged  by  an  absorption,  through  the 
agency  of  osteoclasts,  of  many  of  the  smaller  trabeculae  of  osse- 


THE    CONNECTIVE    TISSUES. 


125 


ous  tissue  and  by  a  partial  absorption  of  the  larger  ones,  the 
primary  marrow  spaces  thus  becoming  secondary  marrow  spaces,  or 
Haversian  spaces.  The  osteoblasts  now  arrange  themselves  in  layers 


Connective " 

tissue. 


Outer  fibrous - 
layer  of 
periosteum. 


/' 


Osteogenetic. 
layer  of 
periosteum. 


Osteoblasts. 


Marrow- 
space. 

Blood-ves-. 
sei. 

Osteoblasts. 


K    ~ 

Remnants  of 

\. 

cartilage 

matrix. 

>-*\r^ 

Bone-cells 

^ 

Osseous 

■r 

matrix 

-^       L         -^ 

^-^ 

Osteoblasts  , 

-'"^ 

Fig  01  —From  a  cross-section  of  a  shaft  (tibia  of  a  sheep) ;  X  55°-  In  the  lower 
part  of  the  figure  is  endochondral  bone-formation  (the  black  cords  are  the  remauis  ol  the 
cartilaginous  matrix) ;  in  the  upper  portion  is  bone  developed  from  the  periosteum. 

about  the  walls  of  the  Haversian  spaces  and  deposit  lamella  after 
lamella  of  bone  matrix,  concentrically  arranged,  until  the  large 
Haversian  spaces  have  been  reduced  to  Haversian  canals.     During 


126  THE    TISSUES. 

this  process  many  of  the  osteoblasts  become  inclosed  in  bone 
matrix,  forming  bone-cells  and  the  blood-vessels  of  the  Haversian 
spaces  remain,  as  the  vessels  found  in  the  Haversian  canals.  The 
spongy  intramembranous  bone  not  absorbed  at  the  commencement 
of  the  formation  of  the  system  of  concentric  lamellae,  remains 
between  the  concentric  systems  as  interstitial  lamellae.  The  circum- 
ferential lamellae  are  those  last  formed  by  the  periosteum.  Calcifica- 
ation  of  the  osseous  matrix  takes  place  after  its  formation  by  the 
osteoblasts. 

From  what  has  been  stated  it  may  be  seen  that  the  shafts  of 
the  long  bones  and  bones  not  preformed  in  cartilage  develop  by  the 
process  of  intramembranous  bone-formation,  while  the  cancellous 
bone  in  the  ends  of  the  diaphysis  and  in  the  epiphyses  is  endochon- 
dral bone.  Further,  that  long  bones  grow  in  length  by  endo- 
chondral bone-development,  and  in  thickness  by  the  formation  of 
intramembranous  bone.  In  the  development  of  the  smaller  irreg- 
ular bones,  both  processes  may  be  engaged  ;  the  resulting  bone  can 
not,  however,  be  so  clearly  defined. 


TECHNIC. 

Ranvier's  Method. — One  of  the  methods  for  examining  connective- 
tissue  cells  and  fibers  is  that  recommended  by  Ranvier  (89)  ;  it  is  as  follows : 
The  skin  of  a  recently  killed  dog  or  rabbit  is  carefully  raised,  and  a  o.  i  ^ 
aqueous  solution  of  nitrate  of  silver  injected  subcutaneously  by  means  of  a 
glass  syringe.  The  result  is  an  edematous  swelling  in  which  the  connective- 
tissue  cells  and  fibers  (the  latter  somewhat  stretched)  come  into  imme- 
diate contact  with  the  fixing  fluid  and  are  consequently  preserved  in  their 
original  condition.  In  about  three-quarters  of  an  hour  the  whole  eleva- 
tion should  be  cut  out  (it  will  not  now  collapse)  and  small  fragments 
placed  upon  a  slide  and  carefully  teased.  Isolated  connective-tissue  cells 
with  processes  of  different  shapes,  having  the  most  varied  relations  to 
those  from  adjacent  cells,  are  seen.  The  fibers  themselves  either  consist 
of  several  fibrils,  or,  if  thicker,  are  often  surrounded  by  a  spirally  encir- 
cling fibril.  By  this  method  numerous  elastic  fibers  and  fat-cells  are  also 
brought  out.  If  a  drop  of  picrocarmin  be  added  to  such  a  teased  prepa- 
ration and  the  whole  allowed  to  remain  for  twelve  hours  in  a  moist 
chamber,  and  formic  glycerin  (a  solution  of  i  part  formic  acid  in  100 
parts  glycerin)  be  then  substituted  for  twenty-four  hours,  the  following  in- 
structive picture  is  obtained  :  All  nuclei  are  colored  red,  the  white  fibrous 
connective -tissue  fibers  pink,  the  fibrils  encircling  the  latter  brownish- 
red,  and  the  elastic  fibers  canary  yellow.  The  peripheral  protoplasm 
of  the  fat -cells  is  particularly  well  preserved,  a  condition  hardly  obtain- 
able by  any  other  method. 

Connective  tissue  with  a  parallel  arrangement  of  its  fibers  is  best 
studied  in  tendon,  those  in  the  tails  of  rats  and  mice  being  particularly 
well  adapted  to  this  purpose.  If  one  of  the  distal  vertebrae  of  the  tail  be 
loosened  and  pulled  away  from  its  neighbor,  the  attached  tendons  will 
become  separated  from  the  muscles  at  the  root  of  the  tail  and  appear  as 
thin  glistening  threads.     These  are  easily  teased  on  a  slide  into  fibers  and 


THE    CONNECTIVE    TISSUES.  12/ 

fibrils.     Such  preparations  are  also  useful  in  studying  the  action  of  reagents 
(see  below). 

The  substance  resembling  mucin  which  cements  the  fibrillse  together 
IS  soluble  in  lime-water  and  baryta-water — a  circumstance  made  use  of 
and  recommended  by  Rollet  (72,  II)  as  a  method  for  the  isolation  of 
connective-tissue  fibrils.  In  necrotic  tissue  the  fibers  show  a  degenera- 
tion into  fibrils  (Ranvier,  89). 

If  connective  tissue  be  heated  in  water  or  dilute  acids  to  120°  C,  and 
the  fluid  then  filtered,  a  solution  is  obtained  from  which  collagen  can  be 
precipitated  by  means  of  alcohol.  This  is  insoluble  in  cold  water,  alcohol, 
and  ether,  but  is  soluble  in  hot  water  and  when  dissolved  in  the  latter  and 
cooled,  becomes  transformed  into  a  gelatinous  substance.  Unlike  mucin 
and  chondrin  this  substance  does  not  precipitate  on  the  addition  of  acetic 
and  mineral  acids.  Tannic  acid  and  corrosive  sublimate  will  cause  pre- 
cipitation, as  also  in  the  case  of  chondrin,  but  not  with  mucin  {yid.  also 
Hoppe-Seyler). 

Elastic  tissue  may  be  obtained'  by  treating  connective  tissue  with 
potassium  hydrate  solution,  and  if  the  alveoli  of  the  lungs  be  treated 
for  some  time  with  this  reagent,  very  small  elastic  fibers  can  be  obtained. 
By  this  means  the  connective -tissue  fibers  are  dissolved,  but  not  the  elastic 
fibers.      Particularly  coarse  fibers  are  found  in  the  ligamenta  subflava. 

According  to  Kühne,  connective  and  elastic  tissues  are  differ- 
ently affected  by  trypsin  digestion — /.  ^.,  alkaline  glycerin -pancreas 
extract  at  35°  C. — white  fibrous  connective  tissue  being  resolved  into 
fibrils,  while  elastic  tissue  is  entirely  dissolved. 

To  F.  P.  Mall  also  belongs  the  credit  for  a  few  data,  which  we 
insert,  as  to  the  different  reactions  which  various  connective-tissue  sub- 
stances show  when  treated  by  the  same  reagents. 

When  a  tendon  is  boiled  it  becomes  shorter,  but  if  it  be  fixed  before 
boiling,  there  is  no  change.  Adenoid  reticulum  shrinks  when  boiled,  but 
after  a  short  time  swells,  and  finally  dissolves.  Both  tendon  and  adenoid 
reticulum  shrink  at  70°  C.  If,  however,  they  be  first  treated  with  a 
0.5%  solution  of  osmic  acid,  the  shrinkage  will  not  take  place  until 
95°  C.  is  reached.  If  the  reticulum  or  the  tendon  has  become  shrunken 
through  heat,  they  are  easily  digested  with  pancreatin,  and  putrefy  very 
readily.  Tendon  fibers  do  not  become  swollen  in  glacial  acetic  acid, 
either  concentrated  or  in  strengths  of  0.05^  or  less,  but  in  strengths 
of  0.5'^  to  25^  they  swell,  and  if  placed  in  a  25^  solution  they  will 
dissolve  in  twenty-four  nours.  They  also  swell  in  hydrochloric  acid  in 
strengths  of  o.i^  to  6^.  In  strengths  of  6^  to  25^  the  fibers  remain 
unchanged  for  some  time,  and  only  dissolve  in  a  concentrated  solution 
of  this  acid.  Reticulated  tissue,  on  the  other  hand,  swells  in  a  3^ 
hydrochloric  acid  solution,  but  remains  unchanged  in  strengths  of  3  'Ji^  to 
10^.  It  dissolves  in  twenty-four  hours  in  solutions  of  25^  and  over. 
After  treatment  with  a  dilute  solution  of  acid,  tendon  dissolves  more  rapidly 
on  boiling  than  does  reticular  tissue. 

Tendon  exposed  to  the  action  of  the  gastric  juice  of  a  dog  does  not 
dissolve  more  rapidly  than  elastic  tissue  ;  but  if  placed  in  an  artificial  solu- 
tion of  gastric  juice,  tendon  dissolves  first,  then  reticular  tissue,  and  finally 
elastic  fibers.  Pancreatin  affects  neither  tendon  nor  reticulated  tissue,  but 
if  boiled,  both  tissues  are  easily  digested  by  its  action.  If  taken  out  of 
the  body,  neither  tendon  nor  reticulum  will  become  affected  by  putre- 
faction. In  the  body,  however,  and  especially  at  high  temperatures 
(37°  C.),  both  tissues  are  decomposed  within  a  few  days. 


128  THE    TISSUES. 

Elastic  fibers  remain  unclianged  in  acetic  acid,  and  even  when 
boiled  in  a  20^  solution  they  only  become  slightly  brittle.  They  are, 
however,  rapidly  destroyed  by  concentrated  hydrochloric  acid,  although 
in  a  \ocjo  solution  at  ordinary  temperature  no  change  is  seen.  In  a  50^ 
solution  the  fiber  is  dissolved  in  seven  days,  and  in  a  concentrated  solu- 
tion in  two  days.  The  inner  substance  of  the  fiber  is  first  attacked,  then 
ihe  membrane.  To  demonstrate  this  membrane,  the  fibers  are  boiled 
several  times  in  concentrated  hydrochloric  acid  and  the  whole  then 
poured  into  cold  water.  Occasionally,  a  longitudinal  striation  of  the 
membrane  is  seen,  indicating  a  fibrillar  structure.  Concentrated  solutions 
of  potassium  hydrate  disintegrate  the  fibers  in  a  few  days  ;  weak  solutions, 
more  slowly.  A  i  ^  solution  of  potassium  hydrate  requires  months  to 
produce  the  effect ;  a  2  ^  solution,  one  month  ;  a  5  ^ ,  three  days  ;  a 
10%,  one  day;  and  20^  to  40^,  only  a  few  hours.  A  weak  solution 
of  potassium  hydrate,  even  when  brought  to  the  boiling-point,  does  not 
dissolve  elastic  fibers,  nor  does  it  cause  them  to  become  brittle.  If,  how- 
ever, they  be  boiled  in  a  5^  or  lo^'  solution  of  potassium  hydrate,  the 
membranes  of  the  fibers  will  be  isolated.  A  cold  20^  solution  has  the 
same  effect  in  one  or  two  days.  Pepsin  induces  a  disintegration  of  the 
contents  of  the  fiber,  leaving  the  membranes  intact. 

To  demonstrate  the  inner  substance  of  elastic  fibers  and  their 
membranes,  magenta  red  has  been  recommended  (a  small  granule  is 
added  to  50  c.c.  glycerin  and  50  c.c.  water).  By  this  method  the 
internal  substance  is  colored  red  while  the  sheath  remains  colorless. 

Orcein,  Unna's  Method. — Make  a  solution  consisting  of  Grübler's 
orcein  i  part,  hydrochloric  acid  i  part,  absolute  alcohol  100  parts.  The 
sections  are  stained  in  a  porcelain  dish.  The  stain  is  heated  over  a 
flame  or  in  an  oven  until  the  stain  becomes  quite  thick.  Rinse  thor- 
oughly in  alcohol,  clear  in  xylol,  and  mount.  Elastic  fibers  stain  a  dark 
brown,  white  fibrous  tissue  a  light  brown. 

Fuchsin-resorcin  Elastic  Fibers  Stain  (Weigert). — A  solution 
containing  i  ^  of  basic  fuchsin  and  2  ^  of  resorcin  is  made  and  brought 
to  boiling.  To  200  c.c.  of  this  solution  there  is  added  25  c.c.  of  liquor 
ferri  sesquichlorati  (Germ.  Pharm.).  Boil  for  about  five  minutes,  stir- 
ring the  meanwhile.  Filter  on  cooling,  and  place  the  filter  paper  and 
the  precipitate  collected  in  a  porcelain  dish  and  add  200  c.c.  of 
95^  alcohol  and  bring  to  boiling.  Filter  on  cooling  and  add  to  the 
filtrate  4  c.c.  of  hydrochloric  acid  and  enough  alcohol  to  bring  it  up  to 
200  c.c.  Stain  sections  for  about  one  hour.  Sections  are  then  washed  in 
alcohol  or  acidulated  alcohol,  or,  better  still,  in  alcohol  to  which  a  few 
crystals  of  picric  acid  have  been  added.  Clear  in  xylol  and  mount. 
Elastic  fibers  are  stained  dark  blue  or  bluish-black  if  washed  in  picric 
alcohol. 

Differential  Stain  for  Connective-tissue  Fibrillae  and  Reticu- 
lum (Mallory). — Fix  tissues  in  corrosive  sublimate  or  in  Zenker's  so- 
lution. (Tissues  fixed  by  other  methods  may  also  be  used,  although  the 
results  are  not  quite  so  satisfactory,  if  the  sections  are  immersed  for  fifteen 
to  thirty  minutes  in  a  saturated  corrosive  sublimate  solution  just  before 
staining. )  The  sections,  which  may  be  cut  in  celloidin  or  paraffin,  are 
stained  for  one  to  three  minutes  in  a  yV%  aqueous  solution  of  acid  fuch- 
sin, rinsed  in  water,  and  placed  in  a  i  ^  aqueous  solution  of  phosphomo- 
lybdic  acid  for  five  to  ten  minutes,  and  then  washed  in  two  changes  of 
water.     They  are  now  stained  in  the  following  solution  for  two  to  twenty 


THE    CONNECTIVE    TISSUES.  1 29 

minutes:  Griibler's  aniline  blue  soluble  in  water,  0.5  gm.  ;  Grübler's 
orange  G,  2  gm.  ;  oxalic  acid,  2  gm.  ;  distilled  water,  100  c.c.  After 
staining,  the  sections  are  washed  in  water  and  dehydrated  in  95^  alcohol, 
blotted  on  the  slide,  and  cleared  in  xylol  and  mounted  in  xylol  balsam. 
The  connective-tissue  fibers  and  reticulum  stain  blue. 

Dr.  Sabin's  modification  of  this  method  deserves  mention.  Fix  in 
Zenker's  fluid,  cut  in  paraffin,  and  fix  sections  to  the  slide  with  the  water 
method.  After  removing  the  paraffin,  stain  sections  in  y-g-^  acid  fuchsin 
until  red,  and  without  washing  fix  in  a  saturated  aqueous  solution  of 
phosphomolybdic  acid  diluted  ten  times  for  about  ten  minutes.  Wash  in 
95%  alcohol  and  stain  for  a  very  short  time  in  thfe  following  solution  : 
Griibler's  aniline  blue  soluble  in  water,  i  gm. ;  orange  G,  2  gm. ;  oxalic 
acid,  2  gm.  ;  boiling  water,  100  c.c.  Wash  in  alcohol,  blot  on  the  slide, 
clear  in  xylol  and  mount  in  xylol  balsam. 

Digestion  Method  for  Demonstrating  the  Connective-tissue 
Framework  of  Organs  and  Tissues  (Mall,  Spalteholz,  Hoehl, 
Flint). — For  bringing  out  the  framework  of  white  fibrous  and  reticular 
fibers  of  organs  and  tissues  digestion  by  means  of  trypsin  may  be  recom- 
mended. For  the  account  here  given  we  follow  Flint.  The  tissues  are 
fixed  in  graded  alcohol,  corrosive  acetic,  or  Van  Gehuchten's  chloroform- 
acetic-alcohol  mixture.  After  complete  dehydration,  small  pieces  of 
tissue,  not  to  exceed  3  mm.  in  thickness,  are  placed  in  paper  cups  and 
dropped  into  a  Soxhlet  apparatus  and  extracted  with  ether  for  a  period 
of  six  to  eight  days  in  order  to  free  the  tissue  of  the  fat.  After  the  fat 
has  been  removed,  the  tissues  are  brought  into  water,  through  graded 
alcohol,  and  then  digested  in  pancreatin.  (Griibler's  pancreatin  is  rec- 
ommended ;  that  of  Park,  Davis  &  Co.  may  be  used.)  The  pancreatin 
solution  to  be  used  is  made  by  adding  as  much  pancreatin  as  can  be  taken 
up  on  the  end  of  an  ordinary  scalpel  handle  to  100  c.c.  of  a  0.5^ 
solution  of  bicarbonate  of  soda.  This  solution  is  changed  every  forty- 
eight  hours.  To  prevent  putrefaction  enough  chloroform  is  added  to 
cover  the  bottom  of  the  dish.  The  digestion  is  continued  until  the  cell- 
ular element  has  been  removed — five  to  ten  days.  It  is  often  necessary 
to  repeat  the  fat  extraction  and  digestion  several  times.  After  the  cellu- 
lar elements  have  been  removed  the  tissue  is  thoroughly  washed  in  flowing 
water,  and  may  then  be  mounted  in  glycerine  and  studied  with  a  stereo- 
scopic microscope,  or  it  may  be  dehydrated  and  imbedded  in  celloidin 
and  sectioned.  Such  sections  may  then  be  stained  in  fuchsin  and  thor- 
oughly washed  in  alcohol ;  this  removes  the  stain  from  the  celloidin, 
leaving  only  the  connective  tissue  stained. 

Sä'äe  Digestion. — The  method  may  also  be  applied  for  digesting 
tissues  on  the  slide.  Fix  as  above  described,  imbed  in  paraffin,  and  cut 
very  thin  sections  which  are  fixed  to  the  slide  by  the  water  method. 
Remove  the  paraffin  and  place  the  sections  from  alcohol  into  the  Soxhlet 
apparatus,  where  they  are  extracted  with  ether  for  a  number  of  hours. 
Bring  the  sections  through  graded  alcohol  into  water,  in  which  they  re- 
main several  hours.  The  sections  are  now  digested  in  the  above-men- 
tioned pancreatin  solution  for  several  hours  to  several  days,  or  until  the 
cellular  elements  have  been  removed.  Wash  carefully  in  water.  The 
remaining  connective  tissue  may  now  be  stained  in  iron-lac  hematoxylin 
or  in  an  aqueous  solution  of  toluidin  blue  or  in  an  aqueous  solution  of 
fuchsin.      Dehydrate,  clear,  and  mount. 


130  THE    TISSUES. 

Fresh  adipose  tissues  can  be  obtained  in  lobules  and  in  small 
groups  of  cells  from  the  mesenteries  of  small  animals.  As  a  rule,  the 
highly  refractive  fat  globule  hides  from  view  the  nucleus  and  protoplasm 
of  the  cell.  The  latter  structures  can  be  brought  out  by  the  subcutaneous 
injection  of  silver  nitrate  solution,  this  forming  the  edematous  elevation 
previously  described.  Fresh  fat  is  soluble  in  ether  and  chloroform, 
especially  if  the  latter  be  heated.  Strong  sulphuric  acid  does  not  dis- 
solve fat.  The  stains  made  from  the  root  of  the  henna  plant  color  fat 
red  (the  color  disappearing  in  ethereal  oils).  Quinolin-blue,  dissolved 
in  dilute  alcohol,  stains  fat  a  dark  blue.  If  a  40%  potassium  hydrate 
solution  be  then  added,  everything  will  become  decolorized  except 
the  fat.  The  most  important  reagent  for  demonstrating  adipose  tissue  is 
osmic  acid  (and  its  mixtures).  Small  pieces  of  adipose  tissue  are 
treated  for  twenty-four  hours  with  a  o.  5  %  to  i  %  osmic  acid  solution  ;  if 
mixtures  containing  osmic  acid  be  used,  the  specimens  are  generally  im- 
mersed for  a  somewhat  longer  period.  The  pieces  are  then  washed  with 
water,  and  should  not  be  placed  directly  into  alcohol  of  full  strength,  as 
all  the  structures  would  then  become  intensely  black  (Flemming,  89),  but 
carried  into  alcohols  of  ascending  strength.  When  treated  in  this  way  the 
globules  of  fat  take  a  more  intense  stain  than  the  other  tissues,  which, 
nevertheless,  are  blackened  to  some  extent.  Fat  that  has  been  subjected 
to  osmic  acid  treatment  dissolves  readily  in  turpentine,  xylol,  toluol, 
ether,  and  creosote,  with  difficulty  in  oil  of  cloves,  and  not  at  all  in 
chloroform.  Such  preparations  are  best  carried  from  chloroform  into 
paraffin.  Fat  that  has  been  stained  with  osmic  acid  can  be  decolorized 
by  nascent  chlorin.  The  specimens  are  placed  in  a  jar  of  alcohol  in 
which  crystals  of  potassium  chlorid  have  been  previously  placed.  Hydro- 
chloric acid  is  then  added  (to  1%)  and  the  vessel  tightly  sealed  (P. 
Mayer,  81). 

L.  Daddi  has  recently  recommended  Sudan  III  as  a  stain  for  fat. 
This  reagent  can  be  applied  in  two  ways  :  ( i )  Either  the  animals  are  fed 
with  the  coloring  matter  for  some  days,  in  which  case  all  the  fat  will  be 
colored  red,  or  (2)  either  fresh  or  fixed  pieces  of  tissue  or  sections  are 
stained.  Fixation  before  staining  must  be  done  in  media  that  do  not  dis- 
solve fat,  as,  for  instance,  Müller' s  fluid.  A  saturated  alcoholic  solution 
of  the  stain  is  used  and  allowed  to  act  from  five  to  ten  minutes.  The 
specimen  is  then  washed  with  alcohol  and  mounted  in  glycerin.  The 
author's  experiments  with  Sudan  have  been  very  satisfactory. 

Thin  lamellae  of  fresh  cartilage  are  examined  after  separating 
them  from  the  soft  parts  and  placing  them  in  indifferent  fluids.  Cartilage 
removed  from  the  hyposternum  or  episternum  or  scapula  of  a  ffog  is 
especially  adapted  for  examination.  Larger  pieces  of  uncalcified  carti- 
lage may  be  used  if  cut  into  sufficiently  thin  sections  with  a  razor  moist- 
ened with  an  indifferent  fluid.  Under  the  microscope  such  sections  show 
a  finely  punctated  background  with  capsules  containing  cartilage-cells, 
provided  the  latter  have  not  fallen  out  in  the  process  of  cutting,  in  which 
case  lacunae  will  be  observed. 

Osmic  acid  and  corrosive  sublimate  are  by  far  the  best  fix- 
ing agents  for  cartilage.  If  the  cartilage  be  calcified,  it  is  fixed  for  some 
time  in  picric  acid,  which  at  the  same  time  acts  as  a  decalcifying  agent. 
Although  alcohol  fixes  cartilage  fairly  well,  it  causes  shrinkage  of  the 


THE    CONNECTIVE    TISSUES.  I3I 

cells.      The   ground    substance  may  be  specifically  colored   by  certain 
reagents,  safranin  producing  an  orange  and  hematoxylin  a  blue  stain. 

On  treating  cartilage  by  certain  methods,  systems  of  lines 
appear  in  its  ground  substance,  possibly  indicating  a  canalicular  sys- 
tem in  the  cartilage.  In  order  to  make  these  structures  visible,  Wolters 
recommends  staining  thin  sections  for  twenty-four  hours  in  a  dilute  solu- 
tion of  Delafield's  hematoxylin  (violet  blue).  They  are  then  treated 
with  a  concentrated  alcoholic  solution  of  picric  acid. 

The  capsules  are  seen  to  best  advantage  if  small  pieces  of  car- 
tilage are  treated  with  z.  \'^/o  solution  of  gold  chlorid. 

Connective-tissue  and  elastic  fibers  in  cartilage  are  easily 
demonstrated  by  staining  the  specimens  with  picrocarmin.  The  con- 
nective-tissue fibers  are  colored  a  pale  pink,  the  elastic  fibers  yellow. 
The  latter  may  also  be  stained  with  a  i  %  aqueous  solution  of  acid 
fuchsin. 

If  a  section  of  fresh  cartilage  be  placed  in  a  weak  solution  of 
iodo-iodid  of  potassium  (Lugol's  solution),  glycogen  can  sometimes 
be  seen  in  the  cartilage-cells,  stained  a  peculiar  mahogany  brown.  If 
elastic  fibers  be  present,  they  also  are  stained  brown,  but  of  a  different 
shade. 

Thin  bone  lamellae,  such  as  occur  in  the  walls  of  the  ethmoidal 
cells,  can  be  cleaned  of  all  the  soft  parts  and  examined  without  further 
manipulation.  If  larger  bones  are  scraped  with  a  sharp  knife,  pieces 
suitable  for  microscopic  examination  are  sometimes  obtained. 

Microscopic  Preparation  of  Undecalcified  Bone. — A  long  bone 
is  thoroughly  freed  from  fat  and  other  soft  parts  by  allowing  it  to  macerate, 
after  which  it  is  thoroughly  washed  and  dried,  thus  freeing  it  from  its 
organic  material.  Then,  by  means  of  two  parallel  cuts  with  a  saw,  as 
thin  a  disc  as  possible  is  cut  out.  The  section  is  now  ground  still  thin- 
ner, either  between  two  hones  or  upon  a  piece  of  glass  covered  with 
emery.  One  surface  of  the  bone  is  then  polished  and  fastened  by  means 
of  heated  Canada  balsam  to  a  thick  square  plate  of  glass  with  the 
polished  side  toward  the  glass.  Care  should  be  taken  that  no  air-bubbles 
are  inclosed  between  the  section  and  the  glass.  As  soon  as  the  specimen 
is  firmly  adherent,  the  other  side  is  ground  upon  the  emery  plate  or  hone, 
during  which  manipulation  the  glass  to  which  the  bone  has  been  fastened 
is  held  between  the  fingers.  As  soon  as  the  section  is  sufficiently  thin 
and  transparent,  it  is  polished.  In  order  to  remove  the  Canada  balsam 
and  powdered  bone  from  the  section,  the  glass  and  bone  are  dried  and 
placed  in  some  solvent  of  Canada  balsam,  such  as  xylol.  This  loosens  the 
specimen  from  the  glass,  after  which  it  is  immersed  in  absolute  alcohol, 
thoroughly  washed,  and  dried  in  the  air.  On  examining  the  bone 
through  the  microscope,  its  lacuna  will  appear  black  on  a  colorless  back- 
ground. The  reason  is,  that  the  air  has  taken  the  place  of  the  evapo- 
rated alcohol  and  the  spaces  appear  black  by  direct  light.  Sections 
thus  prepared  may  be  permanently  mounted  as  follows  :  Small  pieces 
of  dry  Canada  balsam  are  placed  both  upon  a  slide  and  a  cover- 
glass  and  warmed  until  they  have  become  fluid,  then  allowed  to 
cool  until  a  thin  film  forms  over  the  balsam  ;  the  bone  disc  is  then 
placed  upon  the  balsam  on  the  slide  and  quickly  covered  with  the 
cover-glass.     A  firm  pressure  will   evenly  distribute  the  balsam,  and  if 


132  THE    TISSUES. 

the  whole  has  been  done  with  sufhcient  rapidity  the  air  will  have  been 
caught  in  the  open  spaces  of  the  bone  before  the  Canada  balsam  has  had 
a  chance  to  enter  these  spaces. 

Other  substances  may  be  used  to  demonstrate  the  spaces  in 
bone.  Ranvier  (75)  recommends  the  following  method:  A  few  c.c. 
of  a  concentrated  alcoholic  solution  of  anilin  blue  (which  is  soluble  in 
alcohol  and  not  soluble  in  water  and  sodium  chlorid  solution)  are  placed 
in  an  evaporating  dish  containing  the  dry  bone.  The  solution  is  very 
carefully  evaporated,  as  the  alcohol  may  otherwise  ignite.  The  specimen, 
which  will  soon  be  covered  on  both  surfaces  by  a  blue  powder,  is  taken  out 
and  ground  upon  a  rough  glass  plate  until  thoroughly  clean.  While  being 
polished  the  bone  should  be  kept  moist  by  a  solution  of  sodium  chlorid. 
On  heating  in  the  evaporating  dish,  the  air  is  driven  from  the  spaces  and 
replaced  by  the  anilin  blue.  As  already  stated,  anilin  blue  is  insoluble 
in  sodium  chlorid  solution,  and  it  therefore  remains  unaffected  by  the 
latter  during  the  process  of  grinding  and  cleaning.  Hence  it  remains  in 
the  lacunae  and  canaliculi  of  the  bone,  which  then  appear  blue.  The 
specimen  may  either  be  mounted  in  glycerin-sodium  chlorid  and  the  edge 
of  the  cover-glass  sealed  with  varnish,  or  the  section  may  be  washed  for 
a  short  time  in  water  (in  order  to  remove  the  sodium  chlorid),  dried, 
and  finally  mounted  in  Canada  balsam  as  directed. 

A  method  adapted  to  the  study  of  the  hard  and  soft  parts  together 
is  that  first  used  by  von  Koch  in  studying  corals.  The  specimen 
is  first  fixed,  and  if  it  be  a  long  bone,  the  marrow  cavity  should  first  be 
opened  to  permit  the  fixing  agent  to  come  in  contact  with  all  parts  of  the 
tissue.  After  fixing,  the  bone  is  stained  and  then  placed  in  absolute 
alcohol,  and  when  completely  dehydrated  the  pieces  are  placed  in  chloro- 
form, then  in  a  thin  solution  of  Canada  balsam  in  chloroform,  and  finally 
put  into  an  oven  kept  at  a  temperature  of  about  50°  C.  for  from  three  to 
four  months.  By  this  means  the  pieces  are  completely  penetrated  by 
the  Canada  balsam,  and  as  the  latter  becomes  very  hard  on  cooling,  the 
sections  may  be  afterward  ground  without  difficulty.  Long  as  this  pro- 
cedure may  seem,  it  is  still  the  one  which  enables  us  to  see  the  soft 
and  hard  parts  of  bone  in  a  relationship  the  least  changed  by  manipu- 
lation. 

In  bone,  as  also  in  cartilage,  there  sometimes  occur  amorphous 
as  well  as  crystalline  deposits  of  lime-salts.  Upon  the  addition  of  acetic 
acid  the  carbonate  of  calcium  gives  off  bubbles ;  upon  the  addition  of 
sulphuric  acid,  short,  thin  needles  will  be  formed — crystals  of  gypsum. 
Hematoxylin  stains  the  lime-salts  blue,  with  the  exception  of  the  oxalate 
of  lime.  Alkaline  solution  of  purpurin  stains  calcium  carbonate  red. 
Caustic  potash  does  not  affect  lime. 

In  order  to  study  the  organic  constituents  of  bone,  it  must 
first  be  decalcified  and  thus  rendered  suitable  for  sectioning — /.  e. ,  the 
lime-salts  must  first  be  removed,  and  that  without  destroying  the  cellular 
elements  of  the  bone.  The  process  of  decalcification  consists  in  substi- 
tuting the  acids  of  the  decalcifying  fluids  for  those  of  the  bone  salts. 
As  a  consequence,  new  combinations  are  formed,  soluble  in  water  or  in 
an  excess  of  the  decalcifying  acids  themselves. 

The  decalcifying  fluids  most  frequently  used  are  : 
{a)  Hyd7-ochlo7'ic  acid   (1%   aqueous  solution),  used  in  quantities 
amounting  to  about  fifty  times  the  volume  of  the  specimen.    The  solution 


THE    CONNECTIVE    TISSUES.  I  33 

is  changed  daily,  and  the  bone  remains  immersed  until  it  is  soft  enough 
to  be  cut.  This  stage  is  reached  when  a  needle  can  be  introduced  with 
no  resistance. 

{b)  An  aqueous  solution  of  nitric  acid  in  strengths  of  3'y^  to  lo'y/f  ,  ac- 
cording to  the  delicacy  of  the  specimen,  and  of  a  specific  gravity  of  1.4. 
Instead  of  water,  70^  alcohol  may  be  used  as  a  solvent  for  the  acid. 
Thoma  has  recommended  for  this  purpose  a  solution  consisting  of  i 
vol.  nitric  acid  of  a  specific  gravity  of  1.3,  and  5  vols,  alcohol.  This 
fluid  is  changed  daily  and  decalcifies  small  objects  in  a  few  days.  The 
specimens  are  then  washed  several  times  in  70 'y^  alcohol  to  remove 
as  much  as  possible  of  the  acid.  95%  alcohol,  with  the  addition 
of  a  little  precipitated  calcium  carbonate,  has  been  recommended  for 
washing  sections  that  have  been  treated  by  Thoma's  method.  After  from 
eight  to  fourteen  days  the  specimens  are  again  washed  with  clear  95% 
alcohol. 

(^)  The  process  of  decalcification  recommended  by  v.  Ebner  (75)  is 
of  considerable  value,  as  it  also  reveals  the  fibrillar  structure  of  the 
bone  lamellae.  A  cold  saturated  solution  of  sodium  chlorid  is  diluted 
with  2  vols,  of  water,  and  2  '^  of  hydrochloric  acid  added.  This  fluid 
decalcifies  very  slowly,  and  must  either  be  changed  daily  or  a  small 
quantity  of  hydrochloric  acid  occasionally  added.  As  soon  as  the  speci- 
men is  thoroughly  decalcified,  it  is  washed  with  a  half-saturated  solution 
of  sodium  chlorid.  A  little  ammonia  is  now  added  from  time  to  time 
until  the  reaction  of  the  fluid  and  bone  is  neutral. 

(^)  Very  small  pieces  that  contain  very  little  lime-salts,  as,  for  in- 
stance, bones  in  an  embryonal  condition  where  calcification  has  only  just 
begun,  can  be  deprived  of  their  lime-salts  by  means  of  acid  fixing  solu- 
tions like  Flemming's  fluid,  chromic  acid,  picric  acid,  etc. 

(^)  Bone  should  be  first  fixed  in  some  one  of  the  fixing  fluids  and 
then  decalcified. 

Schmorl's  Method  for  Demonstrating  the  Bone  Corpuscles 
and  their  Processes  in  Decalcified  Preparations. — The  tissues  are 
fixed  in  Müller's  fluid  or  in  Miiller's  fluid  with  formalin,  decalcified  in 
V.  Ebner' s  fluid,  and  imbedded  in  celloidin.  The  sections  are  stained 
in  either  of  the  following  thionin  solutions  :  concentrated  50^  alcoholic 
thionin  solution,  10  c.c;  i  per  cent,  carbolic  acid  water,  90  c.c;  or 
concentrated  50 ^^  alcoholic  thionin  solution,  10  c.c;  distilled  water, 
100  c.c;  liquor  ammoniae,  10  drops.  Bring  sections  from  water  into  the 
stain,  in  which  they  remain  from  five  to  ten  minutes  or  longer.  Rinse 
sections  in  water,  and  place  them  in  a  saturated  aqueous  solution  of  pic- 
ric acid  for  one  to  two  minutes  or  longer.  Rinse  in  water  and  wash  in 
70^  alcohol  until  no  more  stain  is  given  off".  Dehydrate  in  alcohol, 
clear  in  xylol,  and  mount  in  balsam.  The  bone  corpuscles  and  processes 
are  stained  brownish-black,  the  ground  substance  yellow,  the  cells  red- 
violet. 

SciwiorV s  method  for  staining  the  boundary-sheaths  of  the  bone  cor- 
puscle: Harden,  decalcify,  imbed,  and  stain  as  in  the  preceding 
method.  After  staining  wash  in  water  for  two  minutes  or  longer  ;  rinse 
in  alcohol  for  one-half  minute,  and  again  rinse  in  water  and  place  the 
sections  in  a  saturated  aqueous  solution  of  phosphomolybdic  or  phospho- 
tungstic  acid  for  three  minutes  or  longer  ;  wash  in  water  which  needs  to 
be  changed  frequently  for  ten  minutes.  The  sections  are  now  placed  for 
three  to  five  minutes  in  a  lo^/o  aqueous  solution  of  liquor  ammoniae,  after 


134  THE    TISSUES. 

which  they  are  washed  in  90%  alcohol,  dehydrated,  cleared  in  xylol, 
and  mounted.  The  boundary-sheaths  are  stained  bluish-black,  the  bone 
cells  dark  blue,  and  the  bone  substance  light  blue. 

Fibers  of  Sharpey. — Sections  treated  by  Ranvier's  method  show  the 
perforating  fibers  of  Sharpey  as  bright,  sharply  defined  ribbons,  appearing 
as  streaks  or  circles,  according  to  the  section  made  (longitudinal  or  trans- 
verse). If  decalcified  specimens  be  first  rendered  transparent  by  glacial 
acetic  acid,  and  then  immersed  for  a  minute  in  a  concentrated  aqueous 
solution  of  indigocarmin,  washed  with  water,  and  then  mounted  in  gly- 
cerin or  Canada  balsam,  the  fibers  of  Sharpey  will  appear  red  and  the 
remaining  structures  blue.  Thin  sections  of  bone  can  be  deprived  of 
their  organic  elements  by  bringing  them  for  from  one -half  a  minute  to  a 
minute  into  a  platinum  crucible  at  a  red  heat.  In  such  preparations  cal- 
cified Sharpey's  fibers  may  be  seen  (Kölliker,  86). 

Virchow's  bone  corpuscles  may  be  isolated  in  the  following 
manner :  Very  thin  fragments  or  discs  of  bone  are  immersed  for  some 
hours  in  concentrated  nitric  acid.  They  are  then  placed  on  a  slide  and 
covered  with  a  cover-glass  ;  pressure  with  a  needle  upon  the  latter  will 
isolate  the  lacunae,  and  occasionally  also  their  numerous  processes,  the 
canaliculi. 


C  MUSCULAR  TISSUE. 

Almost  all  the  muscles  of  vertebrates  have  their  origin  from  the 
middle  germinal  layer.  In  the  simplest  type  the  protoplasm  of  the 
formative  cell  changes  into  contractile  muscle  substance,  the  cell  in 
the  meantime  undergoing  a  change  in  shape  (unstriped  muscle-cell). 
In  other  cases  contractile  fibrils  are  formed  which  are  separated  by 
the  remains  of  the  undifferentiated  protoplasm  (striped  muscle-cells). 
In  this  case  the  cells  either  increase  very  little  in  length  and  possess 
only  a  single  nucleus  (heart  muscle),  or  they  grow  considerably 
longer  and  develop  many  nuclei  (voluntary  skeletal  and  skin 
muscles). 

A  peculiarity  of  muscle-substance  is  that  it  contracts  in  only 
one  direction,  while  undifferentiated  protoplasm  contracts  in  all 
directions. 

J.  NONSTRIATED  MUSCLE-CELLS. 

The  smooth,  unstriped,  or  nonstriated  muscle-cells  belong -to 
involuntary  muscle,  and  are  found  in  the  walls  of  the  intestine, 
trachea,  and  bronchi,  genito-urinary  apparatus,  blood-vessels,  in 
certain  glands,  and  also  in  connection  with  the  hair  follicles  of  the 
skin.  The  involuntary  muscle-cells  are  spindle-shaped  cells,  which 
are  40-200  ix  long  and  3-8  //  broad.  The  longest  are  found  in  the 
pregnant  uterus,  where  they  attain  a  length  of  500  fx.  At  the  thick- 
ened middle  portion  of  the  cell  is  a  long  rod-Hke  nucleus,  typic  of 
this  class  of  cells.  Nonstriated  muscle-cells  are  doubly  refractive 
— anisotropic.  The  cell  substance  is  longitudinally  striated,  the 
striation  being  due  to  relatively  coarse  fibrils  situated  in  the  outer 


MUSCULAR    TISSUE. 


135 


Nucleus. 


Protoplasm. 


portion  of  the  cell  substance  (M.  Heidenhain,  Schaper,  Benda). 
These  fibrils  have  a  longitudinal  course,  and  probably  run  the  en- 
tire length  of  the  cell ;  whether  they  branch  and  anastomose  must 
be  regarded  as  an  open  question.  In  the  interior  of  the  cell  sub- 
stance there  are  found  much  finer  fibrils,  which  branch  and  anasto- 
mose. Between  the  fibrils  there  is 
found  a  homogeneous  substance, 
which  we  may  know  as  the  sarco- 
plasm,  in  which  granules  are  often 
seen,  situated  at  the  poles  of  the 
nuclei.  It  is  generally  stated  that 
nonstriated  muscle-cells  are  united 
into  membranes  and  bundles  by  a 
small  amount  of  intercellular  cement 
substance  which  may  be  darkened  by 
silver  nitrate.  Recent  investigations 
have,  however,  revealed  the  fact  that 
nonstriated  muscle-cells  are  encased  in 
delicate  connective  membranes,  which 
membranes  unite  to  form  compart- 
ment-like spaces,  of  fusiform  shape,  in 
which  the  muscle-cells  are  found. 
These  membranes  are  not  to  be  re- 
garded as  cell-membranes — sarco- 
lemma — since  one  membrane  serves 
as  the  sheath  for  two  contiguous 
muscle-cells  (Schafifer,  v.  Lenhossek, 
Henneberg).  The  existence  of  such 
membranes  is  clearly  shown  in  invol- 
untary muscle  tissue  subjected  to 
trypsin  digestion.  In  such  preparation 
stained  in  iron- lac- hematoxylin  it 
may  be  observed  that  the  membranes 
are  not  complete,  but  are  fenestrated, 
showing  a  varying  number  of  round 
or  oval  openings  (Henneberg).  The 
membranes  are  also  clearly  shown  in 
tissue  fixed  in  corrosive  sublimate  and 
stained  in  Mallory's  differential  con- 
nective-tissue stain,  the  membranes 
showing  as  delicate  blue  lines  while 
the  muscle-cells  are  stained  of  a  red 
or  orange  color.  (See  Fig.  92.)  Ac- 
cording to  certain  observers  (Kultschitzky,  Barfurth),  nonstriated 
muscle-cells  are  thought  to  be  joined  by  intercellular,  protoplasmic 
bridges.  It  may,  however,  be  clearly  shown  that  such  intercellular 
bridges  are  artifacts,  due  to  peripheral  vacuolization  and  to  shrinkage 
of  the  muscle-cells  (Schaffer,   v.    Lenhossek,   Henneberg).      What 


Fig.  92. — Nonstriated  muscle 
from  the  intestine  of  a  cat.  X  300. 
a.  Isolated  muscle-cell  ;  b,  from 
cross-section  of  nonstriated  muscle, 
stained  after  Mallory's  differential 
connective-tissue  stain.  Observe 
the  apparent  difference  in  size  of 
the  cross-cut  cells ;  four  of  the  cells 
show  nuclei ;  the  black  lines  separ- 
ating the  cells  represent  the  connec- 
tive-tissue membranes.  c.  Cross- 
sections  .  of  the  connective-tissue 
membranes  separating  involuntary 
muscle-cells ;  d,  an  area  showing 
so-called  intercellular  bridges  ;  they 
are  attached  to  the  connective  tissue 
membranes  surrounding  the  cells 
(Mallory's  differential  connective- 
tissue  stain). 


136 


THE    TISSUES. 


has  been  described  as  intercellular  bridges  may  readily  be  seen  in 
corrosive  sublimate  preparation,  stained  in  Mallory's  differential 
connective-tissue  stain,  especially  in  portions  of  the  preparation  not 
well  fixed.  In  such  preparation  the  so-called  intercellular  bridges 
end  at  the  connective  membranes  separating  cells,  to  which  they 
are  attached  but  which  they  do  not  penetrate.  Nonstriated  muscle- 
cells  develop  from  the  mesenchyme.  (Exceptions  to  this  statement 
appear  to  be  found  in  the  nonstriated  muscular  tissue  of  the  iris 
[Szili]  and  in  the  sweat-glands,  where  the  muscular  tissue  appears 
to  be  developed  from  ectodermal  cells.)  The  nuclei  of  the  mesen- 
chymal cells  elongate  and  become  rod-shaped,  with  oval  ends,  while 
the  cells  become  spindle-shaped,  the  protoplasm  staining  somewhat 
more  deeply  than  that  of  the  surrounding  mesenchymal  cells. 
Further  details  as  to  the  development  of  nonstriated  muscular  tissue 
are  lacking. 

2.  STRIPED  MUSCLE-FffiERS. 

Soon  after  the  segmentation  of  the  mesoderm  begins,  certain 
cells  of  the  mesoblastic  somites  or  myotomes  commence  the  forma- 
tion of  muscle-substance  in  their  interior,  a  process  which  is  accom- 
panied by  increase  in  the  number  of  nuclei,  the  formation  of  a  mem- 
brane, a  lengthening  of  the  cells,  and  the  appearance  of  fibrils  in 
the  peripheral  protoplasm  of  the  cells. 


Free  ending. 


Nucleus. 


Fig.  93. — Cross- section  of  striated  muscle-fibers  : 
I,  Of  man;  2,  of  the  frog.  The  relations  of  the 
nuclei  to  the  muscle-substance  and  sarcolemma  are 
clearly  visible  ;  X  ^7°- 


Fig.  94. — Muscle-fiber  from 
one  of  the  ocular  muscles  of  a 
rabbit,    showing    its    free    end ; 

XI75- 


Voluntary  or  striated  muscle-cells  are  large,  highly  differen- 
tiated, polynuclear  cells,  which  may  attain  a  length  of  12  cm.,  with 
a  width  of  10— 100  //.  They  are  consequently  known  as  muscle-fibers. 
Their  free  ends  are  usually  pointed ;  the  ends  attached  to  tendon 
rounded  (Fig.  94), 


MUSCULAR    TISSUE.  1 37 

Each  striated  muscle-fiber  consists  of  a  delicate  membrane,  the 
sarcoknivia,  a  muscle  protoplasm,  in  which  are  recognized  ver}-  fine 
fibrils  and  a  semifluid  interfibrillar  substance  (the  sarcoplasm)  and 
the  muscle  nuclei.  The  sarcolemma  is  a  very  delicate,  transparent, 
and  apparently  structureless  membrane,  which  resists  strong  acetic 
acid,  even  after  boiling  for  a  long  time.  If  we  examine  in  an  indif- 
ferent fluid  fresh  muscle-fibers,  the  contents  of  which  have  been 
broken  without  rupturing  the  sarcolemma,  we  may  see  this  sheath 
as  a  fine  glistening  line.     (Fig.  95.) 

The  fibrils  of  the  muscle-protoplasm  constitute  the  contractile 
part  of  the  muscle-fiber.  They  are  exceedingly  fine  and  extend  the 
entire  length  of  the  muscle-fiber.  These  fibrils  are,  however,  not  of 
the  same  composition  throughout,  but  are  made  up  of  segments 
which  show  different  physical  properties  and  stain  differently.  The 
structure  of  the  fibrils  may  be  expressed  in  the  form  of  a  diagram 
(Fig.  96)  giving  the  more  recently  expressed  views  of  the  structure 
of  these  fibrils.  The  fibrils  present  alternating  darker  and  lighter 
segments,  which  taken  together  give  the  striation  which  is  so  char- 


Fig.  95. — Striated  muscle-fiber  of  frog,  showing  sarcolemma. 

acteristic  of  striated  muscle.  The  darker  segments  are  slightly 
longer,  are  doubly  refracting,  anisotropic,  and  in  general  stain  more 
deeply  than  do  the  lighter  segments,  which  are  slightly  shorter  and 
are  singly  refracting,  isotropic.  The  darker  segments,  known  as  the 
transverse  discs,  or  Brücker's  lines,  are  indicated  in  the  diagram  by 
the  letter  q  ;  the  lighter  segments,  known  as  the  intermediate  discs 
of  Krause,  are  indicated  by  the  letter  j.  In  the  intermediate  discs 
of  Krause  there  is  found  a  dark  line,  which  is  doubly  refractive, 
which  is  known  as  Krause's  membrane  (z)  (Grundmembran),  and 
which,  according  to  certain  observers  (M.  Heidenhain,  J.  B.  Mac- 
Callum),  is  continuous  through  the  fibril  bundles,  as  will  be  stated 
more  fully  later.  This  membrane  divides  disc  j  into  two  equal 
parts.  The  transverse  disc  (q)  is  likewise  divided  into  equal  parts 
by  a  narrow,  isotropic  band,  known  as  the  median  disc  of  Hensen, 
and  designated  by  the  letter  h.  In  the  median  discs  of  Hensen — 
H — there  is  found  a  thin  membrane,  known  as  the  median  mem- 
brane of  M.  Heidenhain,  and  designated  as  m,  which,  like  the  mem- 
brane of  Krause,  is  continuous  through  the  fibril  bundles,  uniting 


138 


THE    TISSUES. 


the  fibrils  (M.  Heidenhain).  By  grouping  the  unequally  refracting 
substances  (or  unequally  staining  substances)  a  fibril  may  be  divided 
into  successive  portions  or  protoplasmic  metameres  which  may  be 
termed  sarcomeres  (Schäfer)  and  which  are  bounded  by  the  mem- 
brane of  Krause  (z).  In  such  a  sarcomere  or  muscle-casket  we 
may  recognize,  beginning  with  Krause's  membrane,  z,  an  isotropic 
intermediary  disc,  j  ;  an  anisotropic,  transverse  disc,  q,  divided  by 
a  less  refracting  Hensen's  disc,  h,  into  two  equal  parts,  Hensen's 
disc  showing  the  median  membrane  of  Heidenhain,  m  ;  again  an  iso- 


Fig.  96. — Diagram  of  the 
structure  of  the  fibrils  of  a  stri- 
ated muscle-fiber.  The  light 
spaces  between  the  fibrils  may 
represent  the  sarcoplasm. 


Fig.  c)7. — Diagrams  of  the  transverse  stria- 
tion  in  the  muscle  of  an  arthropod  ;  to  the  right 
with  the  objective  above,  to  the  left  with  the  ob- 
jective below  its  normal  focal  distance  (after  Rol- 
lett,  85):  Q,  Transverse  disc;  /i,  median  disc 
(Hensen)  ;  £,  terminal  disc  (Merkel) ;  JV,  acces- 
sory disc  (Engelmann)  ;  J,  isotropic  substance. 


tropic  intermedian  disc,  j,  and  Krause's  membrane,  z.  Krause's 
membrane,  as  above  stated,  is  continuous  across  the  small  bundles 
into  which  the  fibrils  are  grouped,  and  is  also  attached  to  the  sar- 
colemma  (M.  Heidenhain,  J.  B.  MacCallum).  This  is  shown  to  the 
left  in  Fig.  96,  where  the  sarcolemma  appears  festooned,  with 
Krause's  membrane  attached,  thus  indicating  clearly  the  sarcomeres. 
One  of  the  best  objects  for  the  study  of  transverse  striation  is 
the  muscle  of  some  of  the  arthropods  (beetles).      In  the  striated 


MUSCULAR    TISSUE. 


139 


muscle  of  beetles  and  other  arthropods  there  is,  however,  a  further 
division  into  isotropic  and  anisotropic  substance.  Here  it  will  be 
noticed  that  the  disc  j  is  separated  by  an  anisotropic  disc,  known  as 
the  accessory  disc  of  Engelman,  and  designated  by  the  letter  n,  into 
an  isotropic  disc  j,  next  to  the  anisotropic  transverse  disc  q,  and  an 
isotropic  disc,  known  as  Merkel's  terminal  disc,  and  designated  by 
the  letter  e,  situated  next  to  Krause's  membrane  (z).  (See  lower 
portion  of  Fig.  96.)  The  muscle  fibrils  present  a  different  appear- 
ance when  focused  high  than  they  do  when  focused  low,  as  may  be 
seen  from  the  diagram  given  in  Fig.  97 ;  those  parts  which  appear 
light  on  high  focusing  appear  dark  on  deep  focusing. 


Sarcoplasm. 


Cohnheim's 
area. 


>  Sarcolemma. 


Sarcoplasm. 


Cohnheim's 
area. 


t 


, .  Sarcoplasm. 
--  Fibrils. 


I Sarcolemma. 


Fig.  98. — Transverse  section  through  striated  muscle-fibers  of  a  rabbit.  I  and  3, 
from  a  muscle  of  the  lower  extremity  ;  2,  from  a  lingual  muscle  ;  X  9°°-  I"  2,  Cohn- 
heim's fields  are  distinct;  in  I,  less  clearly  shown ;  in  3,  the  muscle-fibrils  are  more 
evenly  distributed. 


It  has  recently  been  suggested  by  J.  B.  MacCallum  that  Krause's 
membrane  with  the  primitive  fibrils  form  a  continuous  network  in 
the  muscle-fiber,  the  meshes  of  which  Avould  be  fairly  regular,  the 
fibrils  of  such  a  network  which  run  parallel  to  the  long  axis  of  the 
muscle-fiber  being  larger  than  the  cross  fibrils.  Such  a  network  is 
not  to  be-confused  with  a  network  which  may  be  brought  out  on 
staining  striated  muscle-fibers  with  gold  chlorid,  which  network  is 
due,  in  part  at  least,  to  a  staining  of  the  sarcoplasm. 

The  ultimate  fibrils  are  grouped  into  small  bundles  (0.3-0. 5  fJ.  in 


I40 


THE    TISSUES. 


diameter),  forming  the ßbril  bundles  or  rmiscle-columns  of  Kölliker.  In 
the  muscle-columns  the  fibrils  are  so  placed  that  the  larger  segments 
fall  respectively  in  the  same  plane.  (See  Fig.  96.)  The  same  disposi- 
tion of  the  fibrils  prevails  in  all  the  numerous  muscle-columns  form- 
ing a  muscle-fiber,  and  all  the  muscle-columns  bear  such  a  relation 
to  each  other  that  the  larger  segments  of  the  fibrils  fall  in  the  same 
plane.  The  semifluid,  interfibrillar  substance,  the  sarcoplasm,  pene- 
trates between  the  fibrils  of  the  muscle-columns  and  separates  these 
from  each  other  and  from  the  sarcolemma.  In  fresh  preparations  the 
substance  forming  the  fibrils  appears  somewhat  darker  and  dimmer, 
while  the  sarcoplasm  appears  clearer.  The  sarcoplasm  is  found  in 
greater  abundance  between  the  muscle-columns  than  between  the 
fibrils  in  the  columns.  The  sarcoplasm  between  the  muscle-columns 
appears  in  the  form  of  narrower  or  broader  lines,  parallel  to  the 
long  axis  of  the  muscle-fibers,  giving  the  cross-striated  muscle-fiber 
also  a  longitudinal  striation.  The  sarcoplasm  between  the  muscle- 
columns  is  seen  to  best  advantage  in  cross-sections  of  the  muscle- 
fiber.  Here  it  appears  in  the  form 
of  a  network  inclosing  the  mus- 
cle-columns. Thus,  we  have  in 
a  cross-section  slightly  darker 
areas,  the  cross-sections  of  the 
muscle-columns,  known  as  Cohn- 
heiin' s  fields  or  areas,  separated 
by  the  network  of  sarcoplasm. 
(Fig.  98.) 


Fig-  99- — From  a  striated  muscle  of 
man  ;  obtained  by  teasing  ;  X  '  200.  h,  A 
median  disc  lying  in  the  transverse  disc  Q; 
z,  the  membrane  of  Krause  borders  above 
and  below  on  the  light  isotropic  discs. 


Fig.  100.  —  From  a  cross-section 
through  the  trapezius  muscle  of  man, 
showing  dark  fibers  rich  in  protoplasm, 
and  light  fibers  containing  very  little  pro- 
toplasm (after  Schaffer,  93,  II)  :  d,  Dark 
fibers  ;  a,  light  fibers  ;  b  and  c,  transitional 
fibers  from  light  to  dark. 


In  figure  99  is  shown  a  portion  of  a  striated  muscle-fiber  of 
man  very  highly  magnified.  The  larger  and  darker  transverse  disc 
(0  formed  by  the  larger  segments  of  fibrils  is  divided  by  a  light 
line  (h),  Hensen's  median  disc ;  the  clearer  band,  largely  isotropic 
substance,  is  divided  by  a  dark  line,  the  membrane  of  Krause,  z. 

After  a  prolonged  treatment  with  98  fc  alcohol  the  muscle-fibers 


MUSCULAR    TISSUE.  I4I 

of  the  water-beetle  (^Hydrophilus  piccus)  can  be  made  to  separate 
into  transverse  discs  (Rollet,  85).  One  of  these  discs  would  cor- 
respond to  the  segment  Q,  and  it  is  very  probable  that  this  is 
the  portion  which  has  long  been  known  under  the  name  of  Bow- 
man's disc.  Other  reagents,  as  weak  chromic  acid,  cause  a  separation 
of  the  muscle-substance  into  longitudinal  fibrils.  In  this  case  the  discs 
Q  are  split  up  longitudinally  into  a  number  of  very  small  columns 
which  were  at  one  time  regarded  as  the  primary  elements  of  the 
fiber  and  termed  by  Bowman  sarcoiis  elemejits. 

In  adult  skeletal  and  skin  muscle-fibers  of  mammalia  the  posi- 
tions of  the  nuclei  vary.  There  are  muscles  in  which  the  nuclei  are 
imbedded  in  the  sarcoplasm  between  the  muscle-columns  (so-called 
red  muscles,  as  the  semitendinosus  of  the  rabbit) ;  in  other  muscles 
they  lie  immediately  beneath  the  sarcolemma  (white  muscles,  as  the 
semimembranosus  of  the  rabbit ;  Ranvier,  89).  In  the  striated  mus- 
cle-fibers of  the  lower  vertebrates  and  of  mammalian  embryos  the 
nuclei  lie  between  the  fibrillae,  or  muscle-columns.  The  red  muscle- 
fibers  are  rich  in  sarcoplasm,  and  the  fibrils  are  grouped  in  well- 
marked  and  large  muscle-columns  surrounded  by  sarcoplasm  which 
often  contains  granules  of  various  sizes,  the  interstitial  gramdes  of 
Kölliker,  often  especially  abundant  at  the  poles  of  the  nuclei.  The 
white  muscle-fibers  have  a  relatively  small  quantity  of  sarcoplasm. 
In  cross-sections  of  the  light  fibers  the  fibrils  show  as  fine  points,  not 
distinctly  grouped,  and  surrounded  by  the  homogeneous  sarcoplasm. 
Both  varieties  occur  in  almost  every  human  muscle,  and  the  relative 
number  of  each  varies  greatly  in  the  different  muscles  (Schaffer,  93, 
II,  Fig.  100). 

Muscles  with  transversely  striated  fibers  are,  with  the  exception 
of  those  of  the  heart,  subject  to  the  will  of  the  individual,  and 
are  characterized  by  a  rapid  contraction  in  which  the  anisotropic 
substance  increases  in  size  at  the  cost  of  the  isotropic  discs  ;  the 
former  appears  to  play  the  chief  role.  Besides  morphologic  dif- 
ferences, the  red  and  white  muscle-fibers  appear  to  possess  differ- 
ences of  a  physiologic  character,  in  that  the  contraction  in  the  red 


Fig.  loi. — Branched,  striated  muscle-fiber  from  the  tongue  of  a  frog. 

variety  is  slower  than  that  in  the  white  (Ranvier,  80).  Only  the  stri- 
ated muscles  of  the  esophagus,  the  external  cremaster,  and  a  few 
others,  as  well  as  the  somewhat  differently  constructed  muscles  of 
the  heart,  are  involuntary. 


142 


THE    TISSUES. 


Fig.  I02. — Cross-section  of  rectus  abdominis  of  child,  as  seen  under  low  magnification. 


Muscle. 


Tendon. 


>    ,,\'   V 


^"   f'  /     . '  i  '  ' 


Fig.  103, — Part  of  a  longitudinal  section  through  the  line  of  junction  between  muscle 
and  tendon;  X  ^S^-  ^^  the  line  where  the  tendon-fibrils  join  the  sarcolemma  (a),  the 
nuclei  of  the  muscle  are  very  numerous.     Sublimate  preparation. 


MUSCULAR    TISSUE. 


143 


Transversely  striated  muscle-fibers  are  usually  unbranched. 
The  muscle-fibers  of  the  tongue  and  of  the  ocular  muscles  do,  how- 
ever, show  occasionally  communicating  branches  ;  the  same  are 
but  very  rarely  seen  in  other  muscles.  In  regions  where  striated 
muscle-fibers  terminate  under  the  epithelium,  as  in  the  tongue  and 
in  the  skin  of  the  face,  the  end  of  the  fiber  terminating  under  the 
epithelium  is  often  very  much  branched  ;  the  cross-striation  and 
nuclei  may  be  observed  in  the  finest  branches.      (Fig.   loi.) 

Each  muscle-fiber  is  surrounded  by  a  thin  connective-tissue  en- 
velope, the  eiidoinysiiim,  which  binds  them  into  primary  and  second- 
ary bundles,  the  muscle-fasciculi.  These  are  surrounded  by  a 
denser  sheath  of  similar  character,  the  perimysium.  The  muscle  is 
made  up  of  numerous  fasciculi,  all  bound  together  by  a  thicker  con- 
nective-tissue covering,  the  epimysium.     (Fig  102.) 

Blood-vessels  are  very  numerous  in  transversely  striated  mus- 


Nucleus. 


-  Contractile 
substance. 


^^M'^Sf^&i  —  Contractile 


substance. 


Nucleus. 


Fig.  104. 

Longitudinal  and  cross-section  of  muscle-fibers  from  the  human  myocardium,  hard- 
ened in  alcohol  ;  X  640.  The  ma^cle-cells  in  the  longitudinal  section  are  not  sharply 
defined  from  each  other,  and  appear  as  polynuclear  fibers  blending  with  each  other. 
Between  them  lie,  here  and  there,  connective-tissre  nuclei. 

cular  tissue.  One  or  several  arteries  enter  each  muscle  and  form 
superficial  and  deeper  plexuses  by  anastomosis.  In  these  plexuses 
the  arteries  are  accompanied  by  veins.  On  reaching  the  perimysium 
the  arteries  give  off  terminal  branches  which  run  transversely  over 
the  muscle  fascicuH,  at  quite  regular  intervals.  From  these  branches 
precapillaries  and  capillaries  are  given  off  which  have  a  course 
which  is  in  general  parallel  to  the  muscle-fibers ;  these  capillaries 
anastomose  frequently  and  collect  to  form  small  veins,  which  are 
situated  between  the  terminal  arterial  branches,  the  terminal  arterial 
and  venous  branches  thus  alternating  in  such  a  way  that  one  venous 
branch  is  situated  between  two  arterial  branches  or  vice  versa.  The 
veins,  even  the  smallest,  are  provided  with  valves  (Spalteholz). 


144  "^^^    TISSUES. 

At  its  junction  with  tendon  the  muscle-fiber  with  its  sarcolemma 
is  rounded  off  into  a  blunt  point,  the  fibrils  of  the  tendon  being 
cemented  to  the  sarcolemma. 

The  longitudinal  growth  of  muscle-fibers  takes  place  principally 
at  the  distal  ends  of  the  fibers,  at  which  point  their  nuclei  are  numer- 
ous. (Fig.  103,  at«.)  Schaffer  (93,  II)  has  recently  suggested  that 
there  is  a  formative  tissue  between  the  tendon  and  muscle-substance, 
from  which,  on  the  one  hand,  muscle-fibers  are  developed,  and,  on 
the  other  hand,  connective-tissue  fibrils  and  cells  are  formed. 

As  recent  investigations  have  shown,  the  development  of  muscle 
continues  throughout  the  life  of  the  individual.  Muscular  tissue  is 
consequently  to  be  regarded  as  in  a  perpetual  stage  of  transition, 
the  destruction  and  compensatory  reproduction  of  its  elements  going 
on  hand  in  hand.  Its  destruction  is  ushered  in  by  a  process  which 
can  be  compared  to  a  physiologic  contraction.  Nodes  or  thickened 
rings  are  formed,  and  at  these  points  the  muscle-substance  separates 
into  fragments  with  or  without  nuclei  (sarcolytes),  which  are  then 
absorbed,  in  most  cases  without  phagocytic  aid.  This  loss  of  sub- 
stance is  replaced  by  new  elements  developed  from  the  free  sarco- 
plasm,  which  is  characterized  by  rapid  growth  and  increase  in  the 
number  of  its  nuclei.  The  result  is  that  new  elements  are  formed 
which  have  been  called  myoblasts.  The  process  by  which  myo- 
blasts are  changed  into  the  finished  muscle-fibers  is  exemplified  in 
the  embryonal  type  of  development  of  the  tissue. 

Development  of  Voluntary  Muscle-fibers. — The  striated, 
voluntary  muscular  tissue,  as  above  stated,  develops  from  the  myo- 
tomes, segmentally  arranged  differentiated  portions  of  the  meso- 
derm. In  the  myotomes  are  developed  round  or  oval  cells  known 
as  myoblasts,  which  proliferate  by  mitotic  cell  division.  According 
to  the  observations  of  certain  observers,  the  myoblasts  elongate  and 
become  spindle-shaped,  while  the  nuclei  proliferate,  without  an  ac- 
companying division  of  the  cell  body,  to  form  the  muscle-fibers, 
which  may  thus  be  regarded  as  polynuclear  cells  developing  from 
a  single  cell.  Other  observers,  notably  Godlewsky,  state  that  only 
relatively  few  of  the  muscle-fibers  develop  in  this  way,  the  majority 
being  formed  by  a  fusion  of  myoblasts,  forming  a  syncytium,  a 
muscle-fiber  being  thus  a  syncytial  structure  developed  from  a  vary- 
ing number  of  myoblasts. 

The  contractile  fibrils  are  differentiated  from  the  protoplasm  of 
the  differentiating  myoblasts.  When  first  seen,  they  present  a  uni- 
form structure,  and  only  later  can  a  differentiation  into  isotropic  and 
anisotropic  substance  be  recognized.  The  discs  q  and  j  appear 
first ;  the  other  parts  of  the  sarcomeres  somewhat  later.  The  first 
formed  fibrils  divide  longitudinally  to  give  rise  to  new  fibrils.  Em- 
bryonic striated  muscle  tissue,  even  after  striation  of  the  fibers  may 
be  observed,  forms  a  very  compact  tissue  with  only  narrow  inter- 
spaces between  the  cells.  In  the  further  development  of  this  tissue 
certain    of    the    embryonic    muscle-fibers    undergo    degeneration 


MUSCULAR    TISSUE. 


145 


(Bardeen,  Godlewski),  and  mesenchymal  tissue,  blood-vessels,  and 
nerve-fibers  make  their  appearance  between  the  developing  muscle- 
fibers. 

CARDIAC  MUSCLE. 

Cardiac  muscle  or  heart  muscle  is  striated  muscle,  but  differs 
physiologically  and  structurally  from  voluntary  striated  muscle.  It 
resembles  involuntary  muscle  in  that  it  is  not  subject  to  the  will. 
Heart  muscle  after  fixation  with  many  reagents  used  in  the  labora- 
tories, and  when  treated  with  macerating  fluids,  or  subjected  to  the 
action  of  silver  nitrate,  appears  to  consist  of  irregularly  shaped  ob- 
long cells,  cemented  end-to-end  to  form  heart  muscle-fibers;  such 
fibers  appear  to  anastomose  by  means  of  side  processes  possessed  by 
the  cells.  A  number  of  recent  investigators,  notably  v.  Ebner 
and  M.  Heidenhain,  have,  however,  shown  that  what  has  been  re- 
garded as  cement  lines  uniting  cells  are  to  be  otherwise  interpreted, 
since  they  are  known  to  bound  nonnucleated  areas  of  heart  muscle, 
and  since  the  contractile  fibrils  possessed  by  heart  muscle  pass 
through  such  lines  without  interruption.  It  would  appear,  there- 
fore, that  heart  muscle  must  be  regarded  as  a  syncytium  in  which 
no  distinct  and  separate  cells  occur,  but  rather  of  a  complex  plexus 
of  branching  and  anastomosing  fibers  which  differ  in  size  and  shape. 
Heart  muscle-fibers  consist,  as  was  shown  for  voluntary  striated 
muscle-fibers,  of  contractile,  primitive  fibrils,  which  are  grouped  into 
fibril  bundles  or  muscle  columns,  between  which  there  is  found  un- 
differentiated protoplasm,  the  sarcoplasm.  They  are  surrounded  by 
a  sarcolemma,  which  differs,  however,  from  the  sarcolemma  of  volun- 
tary muscle-fibers  in  not  being  so  well  developed.  The  primitive 
fibrils  present  the  same  structure  as  described  for  similar  fibrils  of 
voluntary  muscle,  each  sarcomere  consisting  of  Krause's  membrane, 
z;  two  intermediary  discs,  j;  the  transverse  disc,  q,  bisected  by 
Hensen's  median  disc,  h,  which  in  turn  contains  the  median  mem- 
brane of  Heidenhain,  m.  (See  Fig.  96.)  Krause's  membranes  (z) 
and  the  median  membranes  (m)  extend  across  the  fibril  bundles ; 
the  former  are  attached  to  the  sarcolemma  (M.  Heidenhain).  The 
primitive  fibrils  are  grouped  into  fibril  bundles  or  muscle  columns, 
which  in  cross-sections  are  often  band-shaped  and  are  placed  radially 
with  reference  to  the  center  of  the  heart  muscle-fibers.  The 
sarcoplasm  is  present  in  relatively  larger  quantity  than  in  voluntary 
striated  muscle,  especially  between  the  fibril  bundles,  giving  the 
fibers  a  distinct  longitudinal  striation.  The  primitive  fibrils  pass 
uninterruptedly  through  the  anastomoses  between  the  fibers.  The 
nuclei,  which  are  round  or  oval  and  possess  a  distinct  chromatin 
network,  are  situated  near  the  center  of  the  fibers,  occurring  at  ir- 
regular intervals,  and  are  surrounded  by  an  axial  core  of  undifferen- 
tiated protoplasm,  in  which  are  found  granules  which  stain  in  basic 
stains,  also  fat  droplets,  and,  especially  in  older  individuals,  pigment 
granules.      The  structures  which  have  been  regarded  as  intercellular 


146 


THE    TISSUES. 


cement  lines  may  be  especially  stained  in  certain  anilin  stains.  In 
such  preparations  it  may  be  seen  that  they  often  do  not  extend 
through  an  entire  fiber,  are  frequently  irregular,  often  presenting 
the  appearance  of  steps,  and  now  and  then  involve  only  one  or  two 
fibril  bundles.  They  are  frequently  seen  to  bound  portions  of  a 
muscle-fiber  which  are  nonnucleated.  They  are  looked  upon  by 
M.  Heidenhain  as  representing  growth  areas.  See  Fig.  106,  in 
which  such  intercalated  growth  areas  (cement  lines?)  are  represented 
darker  than  the  remaining  structures. 

Heart  muscle-fibers  are  surrounded  by  delicate  connective-tissue 
sheaths,  very  much  as  described  for  nonstriated  muscle  tissue. 
These  are  well  shown  in  tissue  fixed  in  corrosive  sublimate  and 
stained   after    Mallory's    differential    connective-tissue    stain.       The 


Fig.  106. — Longitudinal  section  of  heart-muscle  of  a  grown  individual,  fixed  in  cor- 
rosive sublimate  and  stained  in  hematein :  a,  Intercalated  disc  (so-called  cement  line); 
b,  nucleus  of  heart  muscle-fiber  ;   c,  red  blood- corpuscles  ;  d,  nucleus  of  blood  capillary. 


fibers  are  grouped  into  bundles  or  fasciculi   which   are  surrounded 
by  internal  perimysium. 

Development  of  Heart  Muscle-tissue. — Heart  muscle-tissue  de- 
velops from  the  mesenchyme,  and  shows  from  the  beginning  a 
syncytial  structure,  in  that  the  cells  are  united  by  protoplasmic 
branches  (von  Ebner,  M.  Heidenhain,  Godlewsky).  As  development 
proceeds,  the  interspaces  between  the  cells  become  smaller  and  the 
protoplasmic  bridges  larger  and  more  prominent,  forming  a  distinct 
syncytium,  through  which  the  nuclei  are  scattered.  In  this  syncytial 
protoplasm  are  developed  the  contractile  fibrils,  which  may  be  traced 
uninterruptedly  for  long  distances.  These  fibrils  show  at  first  a 
uniform  structure,  and  later  differentiate  into  isotropic  and  aniso- 
tropic discs,  Q  and  j   discs  appearing  first  as   in  voluntary  striated 


MUSCULAR    TISSUE.  147 

muscle,  and  later  the  other  parts  of  the  sarcomeres  (Godlewsky). 
It  may  be  stated  that,  according  to  J.  B.  MacCallum  (and  other 
observers),  the  heart-muscle  develops  from  spindle-shaped  cells 
lying  close  together  in  the  protoplasm  of  which  there  is  found  a 
fairly  regular  network.  As  development  proceeds,  fibrils  or  fibril 
bundles  which  run  parallel  to  the  long  axis  of  the  cells  make  their 
appearance  at  the  nodal  points  of  this  network. 

The  muscle-cells  of  the  so-called /^^r.y  of  Purkinje  lie  immediately 
beneath  the  endocardium,  and  are  remarkable  in  that  their  proto- 
plasm is  only  partially  formed  of  transversely  striated  substance,  and 
that  only  at  their  periphery.  Such  cells  are  found  in  great  numbers 
in  some  animals  (sheep),  but  rarely  in  man.  Heart  muscle  has  a 
rich  blood  supply,  which  will  be  considered  more  fully  when  the 
heart  is  discussed  as  an  organ. 

For  the  nerve-endings  in  smooth  and  striated  muscle-fibers  see 
the  chapter  on  Nervous  Tissues. 

TECHNIC. 

Fresh,  striated  muscle-fibers  may  be  isolated  by  teasing  them  in 
an  indifferent  fluid.  After  a  short  time  the  sarcolemma  may  separate  as 
a  very  fine  membrane.  If  a  freshly  teased  muscle  be  placed  in  a  cold 
saturated  solution  of  ammonium  carbonate,  the  sarcolemma  will  become 
detached  in  places  within  five  minutes  (Solger,  89,  III). 

Striated  muscle-fibers  may  be  examined  in  an  extended  condi- 
tion by  placing  an  extremity  in  such  a  position  as  to  stretch  certain 
groups  of  muscles.  A  subcutaneous  injection  of  0.25-0.5  c.c.  of  a  1^0 
osmic  acid  solution  is  then  made.  The  acid  penetrates  between  the  fibers 
and  fixes  them.  Pieces  of  muscle  are  then  cut  out  and  washed  in  dis- 
tilled water.  Teased  fibers,  even  if  not  stained,  will  show  the  stria- 
tion  plainly  if  mounted  in  glycerin.  Muscles  thrown  into  a  state  of 
tetanic  contraction  by  electric  stimulation  may  also  be  fixed  in  this  state 
and  later  examined. 

Cross-sections  of  muscles,  extended  and  fixed  in  osmic  acid, 
also  show  the  relation  of  the  fibrils  to  the  sarcoplasm  (Cohnheim's  fields). 
A  remarkable  quantity  of  sarcoplasm  in  proportion  to  the  number  of 
fibrils  is  seen,  for  instance,  in  the  muscles  which  move  the  dorsal  fin  of 
hippocampus  ;  among  the  mammalia  a  similar  condition  is  found  in  the 
pectoral  muscles  of  the  bat  (Rollett,  89). 

In  the  muscles  of  all  adult  vertebrates  (except  the  mammalia) 
the  nuclei  lie  between  the  fibrils.  In  young  mammalia  they  also  have 
this  position,  but  in  the  adult  animals  only  the  nuclei  of  red  muscles 
are  found  between  the  fibrillae  ;  in  all  other  muscles  the  nuclei  are  under 
the  sarcolemma. 

The  fibrillar  structure  of  muscle-fibers  can  be  seen  by  teasing  old 
alcoholic  preparations,  or  tissue  treated  with  weak  chromic  acid  (o.i^) 
or  one  of  its  salts. 

In  alcoholic  preparations  of  mammalian  muscle,  the  cross- 
striation  is  clearly  seen,  and  is  intensified  by  staining  with  hematoxylin. 
This  stain  colors  everything  anisotropic  in  the  muscle,  but  does  not  affect 
the  remaining  structures.      Similar  results  may  be  obtained  with  other 


148  THE    TISSUES. 

Stains,  such  as  basic  anilin  dyes,  but  not  with  the  same  precision  as  with 
hematoxylin. 

A  certain  species  of  beetle  (^Hydrophilus')  is  admirably  adapted 
for  the  study  of  the  finer  details  of  striation.  The  beetle  is  first  wiped  dry 
and  then  immersed  alive  in  93%  alcohol.  On  examining  in  dilute 
glycerin  after  from  twenty-four  to  forty-eight  hours,  the  substance  of 
its  muscles  will  show  disintegration  into  Bowman's  discs  {yid.  p.  141). 
The  latter  swell  up  in  acids  and  are  finally  dissolved,  as  may  be 
seen,  by  adding  a  drop  of  formic  acid  to  a  specimen  prepared  as  above 
(Rollet,  85). 

In  order  to  study  the  relation  of  muscle  to  tendon,  small  mus- 
cles with  their  tendons  are  put  into  a  35^  potassium  hydrate  solution  for 
a  quarter  of  an  hour,  after  which  the  specimen  is  placed  upon  a  slide  and 
teased  at  the  line  of  junction  of  the  two  tissues.  This  will  separate  the 
muscle -fibers  from  their  respective  tendon -fibrils  (Weismann). 

Similar  results  may  be  obtained  by  immersing  a  frog  in  water 
at  a  temperature  of  55°  C,  in  which  the  animal  soon  dies  with  muscles 
perfectly  rigid.  As  soon  as  the  water  begins  to  cool  (one-quarter  hour) 
the  frog  is  removed  and  a  small  piece  of  its  muscle  cut  out  and  teased  in 
water  on  a  slide  (Ranvier). 

Cardiac  muscle-cells  are  isolated  by  maceration  for  twenty-four 
hours  in  a  20^  solution  of  fuming  nitric  acid  (potassium  hydrate  with  a 
specific  gravity  of  1.3  will  do  the  same  in  one-half  or  one  hour).  The 
margins  of  the  cells  may  be  brought  more  clearly  into  view  by  placing 
pieces  of  heart  muscle  for  twenty -four  hours  in  a  0.5^  aqueous  solution 
of  silver  nitrate  and  then  cutting  into  sections. 

Isolated  fibers  of  Purkinje  are  obtained  by  immersing  pieces 
of  endocardium  (0.5  mm.  in  size)  in  33^  alcohol  and  then  teasing 
them  on  a  slide.  The  sheep's  heart  is  especially  well  adapted  for  this 
purpose. 

Nonstriated  muscle-fibers  are  isolated  in  the  same  way  as  heart 
muscle.  In  thin  cross-sections  (under  5  /"  in  thickness)  of  intestinal 
muscle,  preferably  of  a  cat,  fixed  in  osmic  acid,  the  intercellular  bridges 
may  be  seen  here  and  there  between  the  fibers. 

D«  THE  NERVOUS  TISSUES. 

The  entire  nervous  system,  peripheral  as  well  as  central,  is  com- 
posed of  cells  possessing  one  or  many  processes.  These  cells 
develop  early  in  embryonic  life  from  certain  ectodermal  cells  [neuro- 
blasts) of  the  neural  canal,  which  is  formed  by  a  dorsal  invagination 
of  the  ectoderm.  The  neuroblasts  soon  develop  processes, — many 
of  them  in  loco,  others  only  after  wandering  from  the  neural  canal. 

The  processes  of  the  nerve-cells  are  of  two  kinds  :  (i)  un- 
branched  processes  having  a  nearly  uniform  diameter  throughout, 
with  lateral  offshoots  known  as  collateral  branches  ;  these,  as  we 
shall  see,  generally  form  the  central  part  of  a  nerve-fiber,  and  are 
known  as  neuraxes  (Deiters'  processes,  axis-cylinder  processes, 
neuntes,  neuraxones  or  axones) ;  and  (2)  processes  which  branch 
soon  after  leaving  the  cell-body  and  break  up  into  many  smaller 


THE    NERVOUS    TISSUES.  149 

branches ;  these  are  the  dendrites,  dendrons,  or  protoplasmic  branches. 
In  the  spinal  ganglia  and  the  homologous  cranial  ganglia  these  mor- 
phologic differences  in  the  processes  are  not  observed,  the  neuraxis 
and  the  dendrites  of  each  presenting  essentially  the  same  structure. 

To  the  entire  nerve -cell,  cell-body  and  processes  the  term 
neurone i^^Xdi&y&r,  91)  has  been  applied;  nciira  (Rauber),  or  neu- 
rodendron (KöUiker,  93).  ■,       t^i,  r 

The  neuraxes  of  many  neurones  attain  great  length.  i  hose  ot 
some  of  the  neurones,  the  cell-bodies  of  which  are  situated  in  the 
lower  part  of  the  spinal  cord,  extend  to  the  foot.  In  other  regions 
neuraxes  nearly  as  long  are  to  be  found,  and  in  the  majority  of  neu- 
rones the  neuraxes  terminate  some  distance  from  the  cell-body.  It  is 
therefore  manifestly  impossible  in  the  majority  of  cases  to  see  a  neu- 
rone in  its  entirety.  Usually,  only  a  portion  of  one  can  be  studied 
in  any  one  preparation.  Consequently,  the  more  detailed  descrip- 
tion which  follows  will  deal  with  the  neurone  in  this  fragmentary 
manner.  The  cell-bodies  of  the  neurones,  to  which  the  term 
"nerve-cells"  or  "ganglion  cells"  is  usually  restricted,  the  den- 
drites and  neuraxes,  often  forming  parts  of  nerve-fibers,  and  their 
mode  of  terminating,  will  receive  separate  consideration. 

NERVE-CELLS,  OR  GANGLION  CELLS  j  THE  CELL-BODIES  OF 

NEURONES. 

The  cell-bodies  of  neurones  are  usually  large.  The  bodies  of 
the  motor  neurones  of  the  human  spinal  cord  measure  75  to  150  /i, 
their  nuclei  45  p.,  and  their  nucleoli  1 5  p..  The  smallest  nerve-cells, 
the  neurones  of  the  granular  layer  of  the  cerebellum,  are  4  to  9  //  in 
diameter.  The  protoplasm  of  nerve-cells  shows  a  distinct  fibrillar 
structure  and  the  fibrils  may  be  followed  into  the  processes.  (Fig. 
107.)  Their  nuclei  are  also  large,  with  very  little  chromatin,  but  as 
a  rule  are  supplied  with  a  large  nucleolus. 

After  treatment  by  certain  special  methods,  the  protoplasm  of 
the  ganglion  cells  shows  granules  or  groups  of  granules  which  show 
special  affinity  to  certain  stains,  consequently  known  as  chromato- 
phile  granules  ;  these  are  densely  grouped  around  the  nucleus,  so 
that  the  cell-body  shows  an  inner  darker  and  an  outer  lighter  por- 
tion. These  chromatophile  granules,  also  spoken  of  as  tigroid 
granules  or  as  the  tigroid  substance  (v.  Lenhossek),  as  a  rule  are  not 
arranged  in  concentric  layers,  but  lie  mostly  in  groups,  giving  to  the 
protoplasm  a  mottled  or  reticular  appearance.  In  the  cells  of  the  an- 
terior horns  (man,  ox,  rabbit)  the  granules  join  to  form  flakes,which  are 
also  more  numerous  in  the  region  of  the  nucleus.  In  all  cases  the 
granules  or  flakes  are  continued  into  the  dendrites  of  the  cell.  Here 
they  change  their  shape  into  long  pointed  rods,  with  here  and  there 
nodules,  which  are  probably  the  chief  causes  of  the  varicosities  so 
often  seen  in  dendrites  (Golgi's  method).  The  cell  usually  has  a 
clear,  nongranular  peripheral  border  (not  a  membrane),  and  in  the 


150  THE    TISSUES. 

case  of  large  cells  there  is  a  similar  area  around  the  nucleus,  the 
inner  border  of  which  belongs  to  the  nuclear  membrane.  H.  Held 
has  found  that  the  chromatophile  granules  are  brought  out  by  treat- 
ment with  alcohol  and  acid  fixing  fluids,  but  not  in  alkaline  or  neu- 
tral. They  appear,  according  to  the  treatment,  as  fine  or  coarse 
granules.  They  can  not  be  seen  in  fresh  nerve-cells.  He  conse- 
quently regards  them  as  artefacts — precipitations  of  the  protoplasm 
due  to  reagents  {vid.  A.  Fischer).  At  its  junction  with  the  cell  the 
neuraxis  spreads  out  into  a  cone  which  is  entirely  free  from  granules, 
and  apparently  fitted  into  a  depression  in  the  granular  substance  of 
the  cell  (implantation  cone  or  axone  hillock).  The  shape,  number, 
and  size  of  the  tigroid  granules  vary  with  the  physiologic  activity  of 
neurones.  They  practically  disappear  from  the  neurones  in  certain 
diseased  conditions  or  after  the  administration  of  poisons  which  affect 
more  particularly  nerve-cells  ;  also  after  extreme  fatigue. 

The  cellular  substance  between  the  chromatophile  granules  con- 
sists also  of  very  fine,  highly  refractive  granules,  which  appear  to  be 
arranged  in  a  reticulum  surrounding  the  chromatophile  granules 


Nucleus. 


Nucleolus. 
Fibrillar  structure. 
Medullary  sheath. 


Fig.  107. — Bipolar  ganglion  cell  from  the  ganglion  acusticum  of  a  teleost  (longitu- 
dinal section).  The  medullary  sheath  of  the  neuraxis  and  dendrite  is  continued  over  the 
ganglion  cell ;   X  8°0- 

{vid.  Nissl,  94,  and  v.  Lenhossek,  95),  and  the  recent  observations 
of  Apathy  and  Bethe  make  it  very  probable  that  in  the  intergranular 
substance  of  the  protoplasm  of  the  nerve-cell  there  exist  very  fine 
fibrils  which  may  be  traced  into  the  processes  of  the  cell,  and  from 
the  branches  of  one  neurone  to  and  into  the  branches  of  other  neu- 
rones without  interruption.  It  requires,  however,  further  observation 
before  more  positive  statements  may  be  made  concerning  them. 

Besides  the  granules  above  mentioned,  and  which  are  revealed 
by  special  methods,  there  are  found  in  the  protoplasm  of  many  of 
the  larger  nerve-cells  pigment  granules  of  a  yellow  or  brown  color 
which  stain  black  with  osmic  acid. 

The  dendrites  are  usually  relatively  thick  at  their  origin,  but 
gradually,  as  a  result  of  repeated  divisions,  taper  until  their  widely 
distributed  arborescent  endings  appear  as  minute  threads  of  widely 
different  shapes.  When  treated  by  certain  methods,  they  present 
uneven  surfaces  studded  with  varicosities  and  nodules,  in  contradis- 
tinction to  the  neuraxes,  which  are  smooth  and  straight.  Their  ter- 
minal branches  end  either  in  points  or  in  small  terminal  thickenings. 
The  groups  of  terminal  end-branches  of  a  dendrite  (also  of  a  neur- 
axis) are  known  as  telodendria  (Rauber),  or  end-branches.     The 


THE    NERVOUS    TISSUES. 


151 


branches  of  the  dendrites  form  a  dense  feltwork,  which,  together 
with  the  cell-bodies  of  the  neurones  and  with  other  elemen  s  to  be 
described  later,  constitute  the  gray  substance  (gray  matter)  of  the 
brain  and  spinal  cord.  ,  , 

All  neurones,  with  possibly  a  few  exceptions,  possess  only  a 
sinele   neuraxis.      Neurones  without  a  neuraxis  have   never  been 
found  in  vertebrates.      The  neuraxis   usually  arises  from  a  cone- 
shaped  extension  of  the  cell-body  free  from  chromatophile  granules 
the  implantation  cone  or  axone  hillock,  more  rarely  from  the  base  of 
one  of  its  dendrites,  or  from  a  dendrite  at  some  distance  from  the  cell- 
body.      Its  most  important  characteristics  are  its  smooth  and  regular 
cont':>ur  and  its  uniform  diameter.     At  some  distance  "e  -U 
body,  usually  near  its  termination,  now  and  then  m  its  course,  a 
neuraxis    may    divide    into    two 
equal    parts.      Golgi  (94)  called 
attention  to  the  fact  that  the  neu- 
raxes  of  certain  neurones  (Pur- 
kinje's    cells  in   the  cerebellum, 
pyramidal   cells  of  the  cerebral 
cortex,  and  certain   cells  of  the 
spinal  cord)  give  off  lateral  pro- 
cesses, the  collateral  branches. 


Fig    io8.-Chromatophile  granules  of  Fig.  log.-Nerve-cell  from  rti^J'^te- 

a  gangH^n  cell  from  the  Gasserian  ganglion       rior   horn   of  the   ^P'^f^J^^^^l^''  °^' 
of  a  teleost :    a.  Nucleus  ;  i,  implantation       showing  coarse  chromatophile  flakes. 

cone. 

Two  types  of  cell  are  recognized  according  to  the  disposition  of 
their  neuraxes  :  In  the  first  the  neuraxis  is  continued  as  a  nerve- 
fiber  •  in  the  second  and  rarer  type  it  does  not  long  presence  its 
independence,  nor  is  it  continued  as  a  nerve-fiber,  but  soon  breaks 
up  into  a  complicated  arborization,  the  neuropodm  of  Kolliker  (Q^j- 
The  latter  type  of  cell  occurs  in  the  cortex  of  the  cerebrum  and 
cerebellum  and  in  the  gray  matter  of  the  spinal  cord.  The  cells  ot 
the  two  types  can  be  simply  described  as  having  long  (type  i)  or 
short,  branched  neuraxes  (type  II).  The  neuraxes  of  the  cells  of 
type  I  possess  the  collateral  branches  which  end  m  small  branchmg 

^"^  ^In  its  simplest  form,  a  neurone  consists  of  a  cell-body  and  a  neu- 
raxis with  its  telodendrion.   In  more  complicated  types  one  or  several 


152 


THE    TISSUES. 


dendrites  may  be  present,  as  also  collaterals  from  the  neuraxis,  and 
in  rare  cases  even  several  neuraxes.  According  to  the  number  of 
its  processes,  a  ganglion  cell  is  known  as  unipolar,  bipolar,  or 
multipolar. 


— Dendrite. 


Neurjixis 


Neuraxis. 


Dendrite. — - 


Fig.  no. — Motor  neurones  from  the  anterior  horn  of  the  spinal  cord  of  a  new-born  cat. 

Chrome-silver  method. 

Although  neurones  present  a  great  variety  of  morphologic  dif- 
ferences,— large  and  variously  shaped  cell-bodies  or  small  ones 
scarcely  larger  than  the  nucleus ;  large  and  numerous  dendrites  or 


;;-  Telodendrion. 


-  Dendrite. 


Cell-body. 


—  Neuraxis. 


Fig.  III. — A  nerve-cell  with  branched  dendrites  (Purkinje's  cell),  from  the  cerebellar 
cortex  of  a  rabbit ;  chrome-silver  method  ;   X  ^25. 


few  and  less  conspicuous  ones, — and  although  these  various  forms 
are  widely  distributed  and  intermingled  in  the  different  parts  of  the 
nervous  system,  yet  in  many  regions  there  are  found  nerve-cells  of 
fixed    and    characteristic    morphologic    appearance,    which    would 


THE    NERVOUS    TISSUES. 


153 


enable  a  determination  of  their  source.  A  few  of  the  most  charac- 
teristic types  are  here  figured  and  may  receive  brief  consideration. 
In  the  anterior  horn  of  the  spinal  cord  are  found  large  multipolar 
neurones  (motor  neurones),  with  numerous  dendrites,  which  termi- 
nate after  repeated  branching  in  the  neighborhood  of  the  cell-body, 
while  the  neuraxis  with  its  collateral  branches  proceeds  from  the 
cell-body  and  becomes  a  part  of  a  nerve-fiber.      (Fig.   1 10.) 

In  the  cerebellum  are  found  large  neurones,  discovered  by  Pur- 
kinje, and  known  as  Purkinje's  cells,  with  flask-shaped  cell-body,  from 
the  lower  portion  of  which  arises  a  neuraxis  with  collateral  branches, 


Branching  of  a 
dendrite. 


Neuraxis  and   __ 
collaterals. 


Fig.  112. 


-Pyramidal  cell  from  the  cerebral  cortex  of  man  ;  chrome-silver  method 
a,  b,  c.  Branches  of  a  dendrite. 


from  the  upper  portion  one  or  two  very  large  and  typic  dendrites 
the  smaller  branches  of  which  are  beset  with  irregular  granules. 
(Fig.  III.) 

In  the  cortex  of  the  cerebrum  occur  large  neurones,  each  with  a 
cell-body  the  shape  of  a  pyramid  (pyramidal  cell  of  the  cerebral 
cortex),  from  the  apex  of  which  arises  one  large  dendrite,  and  from 
angles  at  the  base,  or  from  the  sides  of  the  cell-body,  several  smaller 
dendrites.  The  neuraxis  arises  from  the  base  directly  or  from  one 
of  the  basal  dendrites.      (Fig.  112.) 


154  THE    TISSUES. 

In  figure  1 1 3  is  shown  a  neurone  with  relatively  small  cell-body 
and  short  dendrites,  from  the  granular  layer  of  the  human  cere- 
bellum. 

The  function  of  the  dendrites  has  given  rise  to  considerable  dis- 
cussion. Golgi  and  his  school  regard  them  as  the  nutrient  roots  of 
the  cell,  a  theory  which  is  opposed  by  Ramon  y  Cajal  (93,  I ),  van 
Gehuchten  (93,  I),  and  Retzius  (92,  II).  According  to  the  latter, 
all  the  processes  of  the  nerve-cell  are  analogous  structures  ;  they 
pass  out  from  a  sensitive  element,  and  probably  have  a  correspond- 
ingly uniform  function. 

In  the  spinal  ganglia  and  the  homologous  cranial  ganglia,  are 
grouped  the  cell-bodies  of  neurones  (peripheral  sensory  neurones, 
peripheral  centripetal  neurones)  which  differ  in  many  respects  from 
those  above  described.     In   the  peripheral  sensory  neurones  the 


Neuraxis. 


—    a 


—  Telodendrion. 

Nucleus. 


Fig.  113. — Nerve-cell  with  dendrites  Fig.  114, — Ganglion  cell  with  a  pro- 
ending  in  claw-like  telodendria  ;  from  the  cess  dividing  at  a  (T-shaped  process);  from 
granular  layer  of  the  human  cerebellum  ;  a  spinal  ganglion  of  the  frog ;  X  230. 
chrome-silver  method ;  X  ^^O- 

neuraxes  and  dendrites  have  essentially  the  same  structure,  both 
forming  part  of  a  nerve-fiber.  From  a  relatively  large,  nearly  round, 
oval,  or  pear-shaped  cell-body  there  arises  a  single  process,  which, 
at  a  variable  distance  from  the  cell-body,  divides  into  two  branches 
forming  a  right  or  obtuse  angle  with  the  single  process  (T-shaped 
or  Y-shaped  division  of  Ranvier,  78).  Both  of  these  branches  form 
the  central  axis  of  a  nerve-fiber ;  one  of  the  branches  passing  as  a 
nerve-fiber  to  the  spinal  cord  or  brain,  as  the  case  may  be  ;  the  other 
forming  a  nerve-fiber  which  passes  to  the  periphery.     (Figs.  1 14  and 

The  ganglion  cells  of  the  spinal  ganglia  and  homodynamic 
structures  of  the  brain  are  therefore  apparently  unipolar  cells,  but, 
as  Ranvier  has  shown,  their  processes  are  subject  to  a  T-shaped  or 
Y-shaped  division.     The  branches  going  to  the  periphery  are  re- 


THE    NERVOUS    TISSUES. 


155 


garded  as  dendrites,  the  others  as  neuraxes.     As  to  the  significance 
to  be   attached  to  the  single  process,  the  theory  of  v.  Lenhossek 


Fig.  115. Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit ;  stained  in  methylene- 

blue  {intra  vitani). 

(94,  I)  that  it  represents  an  elongated  portion  of  the  cell,  and  that 
therefore  the  origin  of  the  dendrite  and  that  of  the  neuraxis  are  in 
this  case  close  together,  is  very  plausible.  In  the  embryo  these 
ganglion  cells  are  at  first  bipolar,  a  process  arising  from  each  end, 
of  a  spindle-shaped  cell ;  as  de- 
velopment proceeds,  the  two  pro- 
cesses approach  each  other  and 
ultimately  arise  from  a  drawn-out 
portion  of  the  cell  -  body,  the 
single  process.      (Fig,  116.) 

The  sympathetic  ganglia  are 
composed  mainly  of  the  cell- 
bodies  and  dendrites  (also  some 
structures  to  be  mentioned  later) 
of  neurones  of  the  sympathetic 
nervous  system.  In  nearly  all 
vertebrates,  and  with  but  few  ex- 
ceptions in  any  one  ganglion, 
these  neurones  are  multipolar  and 
resemble  morphologically  the 
multipolar  ganglion  cells  of  the  anterior  horn  of  the  spinal  cord, 
though  they  are  somewhat  smaller.   In  the  cell-body  there  may  be  ob- 


Fig.  116. — Three  ganglion  cells  from 
a  spinal  ganglion  of  a  rabbit  embryo.  The 
cells  are  still  bipolar.  Their  processes 
come  together  in  later  stages,  and  finally 
form  the  T-shaped  structure  seen  in  the 
adult  animal ;  chrome  -  silver  method ; 
X170. 


156  THE    TISSUES. 

served  fine  chromatophile  granules  and  a  large  nucleus  and  nucleolus. 
From  the  cell-body  there  proceed  a  varying  number  of  dendrites 
which  branch  and  rebranch  and  terminate,  as  a  rule,  near  the  cell- 
body,  forming  plexuses  in  the  ganglia.  The  neuraxis  arises  either 
directly  from  the  cell-body  from  an  implantation  cone,  or  from  one  of 
the  dendrites  at  a  variable  distance  from  the  cell-body.  (Fig.  1 17.) 
In  nearly  all  ganglia  a  few  unipolar  or  bipolar  cells  are  to  be  found. 
In  the  sympathetic  nervous  system  of  amphibia  the  sympathetic 
neurones  are  unipolar  ;  the  single  process  present  is  the  neuraxis. 

A  most  important  result  of  the  more  recent  investigations  on  the 
nervous  system  is  the  theory  of  the  independence  of  the  neurone. 
Each  neurone  develops  from  a  single  cell  (neuroblast),  and  func- 
tionates as  an  independent  cell  under  physiologic  and  pathologic 
conditions.  Only  very  rarely  has  any  direct  connection  between 
two  neighboring   neurones   been  demonstrated,  so   rarely  that  the 


Fig.  117. — Neurone  from  inferior  cervical  sympathetic  ganglion  of  a  rabbit ;    methylene- 

blue  stain. 

scattered  observations  at  hand  do  not  vitiate  the  above  statement. 
Recent  investigations  have,  however,  shown  that,  while  a  neurone  is 
a  distinct  anatomic  unit,  it  is  always  found  associated  with  other 
neurones.  Nowhere  in  the  body  of  a  vertebrate  does  one  find  a 
neurone  completely  disconnected  from  other  neurones.  This  asso- 
ciation of  one  neurone  with  one  or  several  other  neurones  is  always 
effected  by  a  close  contiguity  existing  between  the  telodendria 
(end-branches)  of  the  neuraxis  of  one  neurone  with  the  cell-body  or 
dendrites  of  one  or  several  other  neurones.  The  telodendrion  of 
the  neuraxis  of  one  neurone  may  form  a  feltwork  inclosing  the  cell- 
body  of  one  or  several  neurones,  forming  structures  known  as 
terminal  baskets  or  end-baskets,  or  the  end  ramifications  of  the 
neuraxis  of  a  neurone  may  come  in  very  close  proximity  to  the 
end-branches  of  the  dendrites  of  one  or  several  neurones.  By  this 
contiguity  of  the  telodendria  of  the  neuraxis  of  one  neurone  with 


THE    NERVOUS    TISSUES. 


157 


the  cell-bodies  or  the  dendrites  of  other  neurones,  they  are,  without 
losino-  their  identity,  linked  into  chains,  so  that  a  physiologic  conti- 
nuity^'exists  between  them.  In  such  neurone  chains  the  dendrites 
are  re^rarded  as  cellulipetal,  transmitting  the  stimulus  to  the  cell  ;  the 
neuraxes  as  cellulifugal,  transmitting  the  impulse  imparted  by  the 
cell  to  the  motor  nerve-endings  or  central  organs  (Kolhker,  93). 
The  entire  nervous  system  may  therefore  be  said  to  be  made 
up  of  such  neurone  chains,  the  complexity  of  which  varies 
<^reatly  according  to  the  number  of  neurones  which  enter  into 
their  construction.  This  subject  will  be  considered  more  fully 
in  a  chapter  on  the  nervous  system. 


Fibrils  of  axial 
cord. 


Neurilemma. 


Segment  of 
Lantermann. 


THE  NERVE-FIBERS. 

The  neuraxes  of  the  cells  of  type  I,  and  the  dendrites  of  the 
peripheral  sensory  neurones  (spinal  ganglia  and  homologous  cranial 
ganglia),  form  the  chief  elements  in  all  the 
nerve-fibers.  In  the  nerve-fibers  they  pos- 
sess a  distinctly  fibrillar  structure.  _  The 
fibrils  composing  them,  the  axis-fibrils,  are 
imbedded  in  a  semifluid  substance,  the 
neuroplasm  (Kupfier,  83,  II)  the  whole 
being  surrounded  by  a  very  delicate 
membrane,  the  axolemma.  In  the  nerve- 
fibers,  the  axis-fibrils  and  the  neuroplasm 
form  axial  cords  which  are  surrounded 
by  a  special  membrane  or  membranes, 
the  presence  or  absence  of  which  serves 
as  a  basis  for  a  classification  of  nerve- 
fibers.  Two  kinds  are  distinguished, 
medullated    and    nonmedullated     nerve - 

fibers. 

In  medullated  nerve-fibers,  the  axial 
cords  (neuraxes  of  cells  of  type  I,  and 
dendrites  of  spinal  ganglion  cells)  are  sur- 
rounded by  a  highly  refractive  substance 

very    similar  to  fat,   which  is    blackened  ,       ,       t        r      1 

in  osmic  acid,  the  so-called  medullary  or  myelin  sheath.  In  a  tresli 
condition  this  sheath  is  homogeneous,  but  soon  changes  and  presents 
secrments  separated  from  each  other  by  clear  fissures.  These  seg- 
ments vary  in  size  and  are  known  as  "  Schmidt-Lantermann-Kuhnt  s 
segments."  On  boiling  in  ether  or  alcohol  the  entire  medullary 
sheath  of  a  nerve-fiber  does  not  dissolve,  but  a  portion  is  left  in  the 
shape  of  a  fine  network  which  is  not  affected  by  exposure  to  the 
action  of  trypsin.  From  the  latter  circumstance  it  has  been  thought 
that  this  network  consists  of  a  substance  ver)^  similar  to  horn  and 
is  therefore  known  as  neurokeratin  (horn-sheath,  Ewald  and  Kuhne). 
On  burning  isolated  neurokeratin,  an  odor  exactly  like  that  of  b^rn- 


Fig.  118. — Longitudinal 
section  through  a  nerve- fiber 
from  the  sciatic  nerve  of  a 
frog;   X830- 


158 


THE    TISSUES. 


ing  horn  is  given  off.  It  is  thought  that  the  meshes  of  this  neuro- 
keratin network  contain  the  highly  refractive  substance  similar  to 
fat,  composing  the  greater  portion  of  the  medullary  sheath.  The 
medullary  sheath  is  interrupted  at  intervals  of  from  80  to  900  //,  the 
constrictions  thus  formed  being  known  as  the  nodes  of  Ranvier.  The 
smaller  the  fiber,  the  less  the  distance  between  the  nodes.  In  a  fiber 
with  a  diameter  of  2  /i  the  internodal  segments  are  usually  about 
90  //  in  length. 

In  peripheral  nerves  the  medullary  sheath  is  in  its  turn  sur- 
rounded by  a  clear,  structureless  membrane,  the  neurilemma  or 
sheath  of  Schwann.  Nerve-fibers  contain  here  and  there  relatively 
long,  oval  nuclei  (neurilemma-nuclei)  which  are  surrounded  by  a 
small  quantity  of  protoplasm,  and  are  situated  in  small  excavations 
between  the  neurilemma  and  the  medullary  sheath.  In  the  higher 
vertebrates  a  single  nucleus  is  found  midway  between  each  two 


Connective  ., 
tissue. 


Fibrils  of  axial 
cord. 


-  Fibrils. 


Fig.  119. — Transverse  section  through  the  sciatic  nerve  of  a  frog;  X  ^^o.  At  a 
and  (^  is  a  diagonal  fissure  between  two  Lantermann's  segments  ;  as  a  result,  the  medul- 
lary sheath  here  appears  double.      (Compare  Fig.  1 1 8.) 

nodes  ;  in  the  lower  vertebrates  (fishes)  several  scattered  nuclei 
(5-16)  may  be  found  in  each  internodal  segment.  At  the  nodes, 
where  the  medullary  sheath  is  interrupted,  the  neurilemma  is 
thickened  and  contracted  down  to  the  axial  cord  (contraction-ring). 

Just  beneath  the  contraction-ring,  Ranvier  found  that  the  axis- 
cylinder  presents  a  slight,  biconic  swelling  {renflement  biconique). 
Thus  the  sheath  of  Schwann  represents  a  continuous  tube  through- 
out the  length  of  the  fiber  in  contrast  to  the  medullary  sheath.  In 
the  nerve-fibers  of  the  spinal  cord  and  brain  there  is  no  neurilemma, 
although  the  medullary  sheath  is  present. 

In  the  fresh  nerve-fiber  the  axial  cord  fills  the  space  (axial 
space)  within  the  medullary  sheath,  and  appears  transparent. 
After  treatment  with  many  fixing  fluids  the  neuroplasm  coagulates 
and  shrinks,  no  longer  filling  the  entire  axial  space,  but  appears  in 
the  latter  as  a  wavy  cord  composed  of  an  apparently  homogeneous 


THE    NERVOUS    TISSUES. 


159 


mass,  the  fibrillje  of  which  are  no  longer  recognizable.  Such  pic- 
tures, which  formerly  were  supposed  to  represent  the  normal  condi- 
tion of  the  nerve-fibers,  gave  rise  to  the  conception  of  an  axis-cyl- 
inder (vid.  Technic).  That  which  is  known  as  an  axis-c}'linder  is 
therefore,  in  reality,  the  changed  contents  of  the  axial  space.  It  may 
be  stated,  however,  that  the  term  axis-cylinder  is  still  much  used, 
since  the  methods  commonly  employed  in  the  investigation  of  the 

nervous  system  do  not 
preserve  the  axial  cord 
in  its  integrity,  but  nearly 
always  result  in  the  for- 
mation of  an  axis-cylin- 
der. Consequently,  al- 
though we  shall  make 
use  of  the  term,  its  limit- 
ations are  to  be  kept  in 
mind. 

Medullated     nerve  - 
fibers  vary  greatly  in  di- 


Ranvier's 
node. 


•  Nucleus. 


Fig.  120. — Medullated  nerve-fibers  from  a  rabbit, 
varying  in  thickness  and  showing  internodal  segments 
of  different  lengths.  In  the  fiber  at  the  left  the  neuri- 
lemma has  become  slightly  separated  from  the  under- 
lying structures  in  the  region  of  the  nucleus ;  X  I4°' 


Fig.  121. — Remak's  fibers 
(nonmedullated  fibers)  from  the 
pneumogastric  nerve  of  a  rabbit ; 
X360. 


ameter,  but  whether  this  points  to  a  corresponding  variation  in 
function  has  not  been  fully  decided.  Fine  fibers  possess  a  diameter 
of  2—4//,  those  of  medium  size  4—9  fi,  and  large  fibers  9—20  // 
(Kölliker,  93).  A  division  of  medullated  fibers  during  their  course 
through  a  nerve  is  relatively  rare.  The  greater  number  of  fibers  pass 
unbranched  from  their  central  origin  to  the  periphery,  and  only  when 
in  the  neighborhood  of  their  terminal  arborization  do  they  begin  to 
divide.     A  point  of  division  is  always  marked  by  a  node  of  Ranvier. 


l6o  .  THE    TISSUES. 

The  segmental  structure  of  nerve-fibers  would  seem  to  give 
the  impression  that  they  are  formed  by  a  number  of  cells  fused  end 
to  end.  After  what  has  been  said  with  regard  to  ganglion  cells  and 
their  processes,  this  can  be  the  case  only  so  far  as  the  nerve-sheaths 
are  concerned.  According  to  this  theory,  the  formative  cells  of  the 
latter  gather  in  chains  along  the  neu  raxes  or  dendrites,  forming  a 
mantle  around  them,  and  in  the  adult  nerve-fibers  taking  the  shape 
of  the  segments  or  internodes  just  described  (His,  87  ;  Boveri,  85). 
The  points  at  which  the  sheath-cells  are  joined  would  then  corre- 
spond to  the  nodes  of  Ranvier.  Other  investigators  have  concluded 
that  the  whole  nerve-fiber  is  developed  from  a  terminal  apposition 
of  ectodermal  cells.  In  this  case  not  only  the  sheaths  of  the  fibers 
but  also  the  corresponding  portions  of  the  nerve  processes  are 
formed  by  them  (Kupffer,  90).  In  both  theories  the  neurilemma 
corresponds  to  the  cell-membrane  ;  in  the  former  the  neurilemma 
nucleus  corresponds  to  that  of  the  sheath -forming  cell,  in  the  latter 
to  that  of  the  formative  cell  of  the  whole  nerve  segment.  It  should 
be  noticed  that,  according  to  the  second  theory,  a  fiber  segment  is 
the  product  of  a  single  cell,  while  according  to  the  first  it  is  evolved 
from  atjeast  two  cells  (ganglion  cell  (process)  and  sheath-forming 
cell).      The  former  theory  is  now  very  generally  accepted. 

The  nonmedullated  nerve-fibers,  Remak's  fibers,  possess  no 
medullary  sheath  ;  the  axial  cord  shows  nuclei  which  can  be  re- 
garded as  belonging  to  a  thin  neurilemma.  The  majority  of  the 
neuraxes  of  the  neurones  of  the  sympathetic  nervous  system  are  of 
this  structure,  although  small  medullated  nerve-fibers  (the  neuraxes 
of  sympathetic  neurones)  are  found  in  certain  regions. 

All  nerve-fibers,  medullated  as  well  as  nonmedullated,  in  the 
central  and  peripheral  nervous  systems  lose  the  sheaths  here  de- 
scribed before  terminating ;  the  axis -cylinders  (axial  cords)  ending 
without  special  covering  (naked  axis-cylinders).  These  terminal 
branches  are,  in  fixed  and  stained  preparations,  beset  with  small 
thickenings — varicosities — which  vary  greatly  in  size  and  shape. 
Nerve-fibers  presenting  such  appearances  are  spoken  of  as  varicosed 
fibers.  The  varicose  enlargements  may  be  regarded  as  small 
masses  of  neuroplasm  ;  the  fine  uniting  threads,  as  representing  the 
axial  fibrils. 

In  the  peripheral  nervous  system  the  nerve-fibers  are  grouped 
to  form  nerve -trunks.  The  nerve-fibers,  as  has  been  stated  and  as 
will  be  seen  from  the  diagram  (Fig.  122)  on  the  next  page,  are  the 
neuraxes  of  neurones,  the  cell-bodies  of  which  are  situated  in  the 
spinal  cord  or  brain  and  in  the  sympathetic  ganglia,  and  the  den- 
drites of  peripheral  sensory  neurones,  the  cell-bodies  of  which  are 
found  in  the  spinal  and  homologous  cranial  ganglia. 

In  the  nerve -trunks  the  nerve-fibers  are  gathered  into  bundles 
termed  funiculi.  The  nerve-fibers  constituting  such  a  bundle  are 
separated  by  a  small  amount  of  fibro-elastic  tissue,  containing  here 
and  there  connective -tissue  cells,  the  endoneurium.    This  is  continu- 


THE    NERVOUS    TISSUES. 


I6l 


ous  with  a  dense,  lamellated  fibrous  sheath  surrounding  each  funicu- 
lus, the  perineurium.  Between  the  lamella;  of  this  sheath  are  lymph- 
spaces,   communicating  with  the   lymph-clefts    found  between  the 


Neuraxis  of  peripheral 
sensory  neurone. 


Dendrite  of  per- 
ipheral s  e  n  - 
sory  neurone. 


Nerve-trunk.   


Spinal  ganglion 


Anterior  horn  of  gray  matter  of 

spinal  cord. 
Neuraxis  of  peripheral  motor 

neurone. 

—  Sympathetic  ganglion. 


Neuraxis  of  sympathetic  neurone. 
Fig.  122. Diagram  to  show  the  composition  of  a  peripheral  nerve-trunk. 


Epineurium. 


— ^ Perineurium. 

Fig.   123.— Part  of  a  cross-section  through  a  peripheral  nerve  treated  with  alcohol. 
The  small  circles  represent  the  cross- sections  of  medullated  nerve-fibers  ;  the  axis-cylin- 
ders show  as  points  in  their  centers.     The  nerve  is  separated  by  connective  tissue  into 
large  and  small  bundles — funiculi ;   X  75- 
II 


102  THE    TISSUES. 

nerve-fibers  of  the  funiculi ;  consequently,  the  lamellae  are  covered 
by  a  layer  of  endothelial  cells.  In  the  larger  funiculi,  septa  of 
fibrous  connective  tissue  pass  from  the  perineurial  sheath  into  the 
funiculi,  dividing  them  into  compartments  varying  in  shape  and  size  ; 
these  are  spoken  of  as  compound  funiculi.  The  funiculi  of  a  nerve- 
trunk  are  bound  together  by  an  investing  sheath  of  loose  fibro-elastic 
tissue,  continuous  with  the  perineurial  sheaths,  which  penetrates 
between  the  funiculi,  and  which  contains  fat-cells,  blood-vessels,  and 
lymph-vessels ;  the  latter  are  in  communication  with  the  lymph- 
spaces  of  the  perineurial  sheaths. 

When  a  nerve-trunk  divides,  the  connective-tissue  sheaths  above 
mentioned  are  continued  on  to  the  branches,  and  this  even  to  the 
smallest  offshoots.  Thus,  single  fibers  even  possess  a  connective- 
tissue  sheath, — Henle's  sheath, — which  consists  of  a  few  connective- 
tissue  fibers  and  of  flattened  cells. 


PERIPHERAL  NERVE  TERMINATIONS. 

According  to  the  character  of  the  peripheral  organs  in  which 
the  telodendria  of  nerve-fibers  (neuraxes  of  type  I  cells  and  dendrites 
of  spinal  ganglion  cells)  occur,  the  nerve-fibers  are  known  as  motor 
and  sensory  nerve-fibers,  the  terminations  as  motor  and  sensory 
nerve-endings. 

Motor  Nerve- endings  (the  Telodendria  of  Ferve-fibers  Ending 
in  Muscle  Tissue). — The  motor  nerve-endings  in  striated,  voluntary 
muscle  tissue  will  first  be  considered.  The  motor  nerve-endings 
in  voluntary  muscle  tissue  are  the  endings  of  neurones  (peripheral 
motor  neurones),  the  cell-bodies  of  which  are  situated  in  the  ventral 
horns  of  the  spinal  cord  and  in  the  medulla.  The  neuraxes  of  these 
cells  leave  the  cerebrospinal  axis  as  medullated  nerve -fibers  (motor 
fibers)  which,  after  branching,  end  in  the  muscle-fibers  in  the  so-called 
motor  endings.  In  figure  124  is  represented,  by  way  of  diagram, 
a  complete  peripheral  motor  neurone.  Each  motor  nerve  -  fiber 
branches  repeatedly  before  terminating,  although  this  branching 
does  not  often  take  place  until  near  the  termination  of  the  nerve- 
fiber.  Kölliker  estimates  that  in  the  sternoradialis  of  the  frog,  each 
motor  fiber  innervates  about  twenty  muscle-fibers  ;  but  whether  this 
number  may  be  regarded  as  the  average  number  of  muscle-fibers 
receiving  their  motor  nerve-supply  from  one  motor  neurone  can  not 
be  stated  with  any  degree  of  certainty  at  the  present  time. 

Each  motor  ending  represents  the  termination  of  one  of  the  ter- 
minal medullated  branches  of  a  motor  nerve-fiber.  The  neuraxis  of 
this  fiber  passes  under  the  sarcolemma  and  terminates  in  a  teloden- 
drion  (end-brush)  in  an  accumulation  of  sarcoplasm,  in  which  are 
found  numerous  muscle  nuclei,  forming  a  more  or  less  distinct  ele- 
vation on  the  side  of  the  muscle-fiber,  Doyere's  elevation.  The 
medullary  sheath  accompanies  the  nerve-fiber  until  it  passes  under 
the  sarcolemma,  when   it  stops  abruptly.     The  neurilemma  of  the 


MOTOR    NERVE-ENDINGS. 


163 


nerve-fiber  becomes  continuous  with  the  sarcolemma  of  the  muscle- 
fiber  at  the  place  where  the  neuraxis  passes  under  the  sarcolemma. 
Henle's  sheath  continues  over  the  motor  endmg  as  a  thm  sheath, 
containing  here  and  there  flattened  nuclei,  the  tdolmmia  nucleu 

With  the  majority  of  the   reagents  used   to  bring  to  view  the 
motor  endings,  notably  chlorid  of  gold,  the  sarcoplasm,  m  which 


Neuraxis.  - 


Medullary  sheath. 


Nucleus  of  neurilemma. 


Motor  ending, 


Dendrite. 


=r-     Collateral  branch. 
Neurilemma. 


Node  of  Ranvier. 
Internodal  segment. 


Axis-cylinder  of  medullated 
nerve-fiber. 


Muscle-fibers. 


Fig,  124.— Diagram  of  peripheral  motor  neurone. 

thetelodendrion  of  the  nerve-fiber  is  found,  has  a  granular  appear- 
ance and  is  consequently  differentiated  from  the  remainmg  saico- 
Dksm  of  the  muscllfiber  To  this  the  term  gramdar  sole  pate  has 
been  appled  The  nuclei  contained  therein  being  known  ^ssolenucln 
the  whok  en^^^^^    as  the  motor  end-plate.     If  the  above  interpreta- 


164  THE    TISSUES. 

tion  of  the  structure  of  the  motor  nerve-ending  is  correct,  there 
would  seem  to  be  no  reason  why  the  sarcoplasm  in  which  the  telo- 
dendria  occur  should  be  considered  other  than  the  sarcoplasm  of 
the  muscle-fiber,  the  nuclei  as  muscle-nuclei ;  the  terms  motor  end- 
plate,  granular  sole  plate,  and  sole  nuclei  would  therefore  seem  un- 
necessary and  misleading.  It  may  be  stated  in  this  connection  that 
Bardeen  has  recently  shown  that  in  teased  muscle-tissue  subjected 
to  trypsin  digestion  the  muscle  substance  may  be  removed  from 
the  fiber  leaving  the  sarcolemma  and  on  its  inner  surface  a  por- 
tion of  the  nerve-ending,  with  the  neurolemma  continuous  with  the 
sarcolemma.  He  has  also  shown  that  the  motor  ending  is  in  part 
differentiated  in  connection  with  developing  muscle-fibers  before 
a  sarcolemma  can  be  shown  on  such  fibers.  In  figures  126  to 
130  are  shown  motor  nerve -endings  from  several  vertebrates  as 
seen  when  stained  with  gold  chlorid. 

The  mass  of  sarcoplasm  in  which  the  neuraxes  terminate  as 
above  described  is  about  40  to  60  [x  long,  40^  broad,  and  6  to  10  // 
thick  ;  these  dimensions  vary  greatly,  however  ;  they  may  be  greater 
or  less  than  the  averages  here  given. 

In  amphibia  the  motor  nerve-endings  are  not  so  localized  as 
in  the  majority  of  vertebrates,  as  above  described,  but  are  spread 
over  a  relatively  greater  surface  of  the  muscle-fiber,  and  there  is  no 
distinct  accumulation  of  the  sarcoplasm,  and  the  muscle-nuclei  ar^ 


Fig.  125. — Motor  nerve-ending  in  voluntary  muscle  of  rabbit,  stained  in  methylene- 
blue  {intra  vitani)  (Huber,  DeWitt,  "Jour.  Comp.  Neurol.,"  vol.  vil)  :  A,  Surface 
view  ;  B,  longitudinal  section  through  motor  ending  ;  C,  cross-section  :  a,  a,  a,  neuraxes 
of  nerve-fibers  ;  s,  s,  s,  sarcolemma  ;  «/, ;?/,  neurilemma  ;  d,  Doyere'  s  elevation  ;  m  n , 
muscle  nuclei ;   /  n,  telolemma  nucleus. 

relatively  less  numerous.  The  telodendrion  of  the  nerve-fiber  is, 
however,  under  the  sarcolemma,  between  it  and  the  contractile  sub- 
stance of  the  muscle-fiber.      (Fig.  131.) 

Usually  only  one  motor  ending  is  found  on  each  striated  muscle- 
fiber.  This  may  be  situated  near  the  center  of  the  muscle-fiber  or 
at  a  variable  distance  from  the  center,  nearer  one  or  the  other  of 
its  extremities.  Now  and  then  two  nerve-endings  are  found  on 
one  muscle-fiber,  in  which  case  the  nerve-endings  are  found  in  close 
proximity. 


MOTOR    NERVE-ENDINGS. 


165 


-  So-called 
granular 
sole. 

-  Nerve 
end- 
brush. 

^  —    Muscle- 
fiber. 


^^^1  fi^-nr^-^-  -    Nerve. 


Fig.  126. 


Fig.  127. 


Nerve. 


So-called 
granular 
sole. 
Kfni'iJ^*/*'^'^""'**«* End-brush. 

|[|ü&!;^;' 'llil/:;-!  I..]  Muscle- 


fiber. 


^       So-called 
-^ —      granular 
#.'  sole. 

—    End-brush. 


Figs.  128  and  129. 

Figs.  126-130.— Motor  endings  in  striated  voluntary  muscles. 
Fig  126  from  Pseiidopus  Pallasii:  X  160.  Fig.  127,  from  Laccrta  viridis;  X  160. 
Figs  lis  and  129,  from  a  guinea-pig;  X  700.  Fig.  130,  from  a  hedge-hog;  X  1200. 
As  a  consequence  of  the  treatment  the  arborescence  is  shrunken  and  mterrupted  in  its 
continuity  In  Figs.  126  and  127  the  end  plate  is  considerably  larger  than  in  12S  and 
12Q  In  Fig  126  it  is  in  connection  with  two  nerve-branches.  Fig.  130  shows  a 
section  throu|h  an  end-plate.  The  latter  is  bounded  externally  by  a  sharply  defined 
line,  which  can  be  traced  along  the  surface  of  the  muscle-fiber.  This  is  to  be  regarded 
as  the  sarcolemma. 


1 66 


THE    TISSUES. 


Heart  muscle  and  no7istriated  muscle  receive  their  motor  nerve- 
supply  from  neurones  of  the  sympathetic  nervous  system.  The 
cell-bodies  of  these  neurones  are  situated  in  sympathetic  ganglia  ; 
the  neuraxes,  the  majority  of  which  form  nonmedullated  nerve- 
fibers,  branch  repeatedly,  forming  primary  and  secondary  plexuses 
which  surround  the  larger  or  smaller  bundles  of  heart  muscle-fibers 
or  involuntary  muscle-cells.  From  these  plexuses,  naked,  vari- 
cosed  axis-cylinders,  or  small  bundles  of  such,  penetrate  between 
the  heart  muscle-fibers  or  involuntary   muscle-cells,  also  forming 


Fig.  131. — Motor  nerve-ending  in  striated  voluntary  muscle  of  a  frog  ;  methylene- 
blue  stain  {intra  vitatn)  (Huber,  DeWitt)  :  A,  Surface  view;  B,  cross-section;  s,s, 
sarcolemma  ;  nl,  neurilemma. 


Jr-u^U 

r> 

1 

y 

(  J 

•>^ 

V. 

\ 

■:■     i 

-i 

.,  /  /     "'■'». 

1 

I    \ 

■^ 

^± 

j 

A 

ft 

Heart 

muscle  cell 

i;  . 

^ 

L^„. 

c^criQ}^ 

w 

.......,:.  ..| 

', 

— 

muscle  era  ' 

1- 

_  riuAUus    ; 

f 

- 

h 

\ 

i 

3mUL            ; 

TZereefihtr     \ 

ii.-«'' 

Fig.  132. — Motor  nerve-ending  on 
heart  muscle-cells  of  cat  ;  methylene-blue 
stain  (Huber,  De  Witt). 


Fig.  133. — Motor  nerve-ending  on 
involuntary  nonstriated  muscle-cell  from 
intestine  of  cat ;  methylene-blue  stain 
(Huber,  De  Witt). 


plexuses.  The  fine  fibers  of  this  terminal  plexus  give  off  from 
place  to  place  small,  lateral  twigs,  which  end  on  the  muscle-fiber 
and  muscle-cells.  In  heart  muscle  these  lateral  twigs  may  end  in 
one  or  two  small  granules,  or  in  a  small  cluster  of  such  granules 
(Fig.  132);  in  involuntary,  nonstriated  muscle  the  ending  is  very 
simple,  the  small  lateral  twigs  terminating  in  one  or  two  small 
granules.     (Fig.  133.) 

Sensory  Nerve-endings. — The  sensory  nerve-endings  are,  in 
their  essentials,  the  peripheral  telodendria  of  dendrites  of  peripheral 


SENSORY    NERVE-ENDINGS. 


167 


sensory  neurones.  The  cell-bodies  of  such  neurones,  as  has  been 
stated,  are  found  in  the  spinal  and  homologous  cranial  ganglia. 
Of  the  two  branches  arising  from  the  single  process  possessed  by 
each  peripheral  sensory  neurone,  the  one  going  to  the  periphery  is 
regarded  as  the  dendrite  and  forms  the  axis-cylinder  of  a  medullated 
nerve-fiber,  such  nerve-fibers  constituting  the  sensory  nerves  of  the 


Nucleus  and 
nucleolus. 


Cell-body. 


Process  of  cell 


Neuraxis,  ends  in  spinal 
cord  or  brain. 


T-shaped  division  of 
Ranvier. 


Dendrite,  a  sensory  nerve- 
fiber  in  nerve-trunk. 


Telodendrion  of 
terminal  branch 
of  dendrite. 


if  iS<m^  ^-> 

Fig.  134. — Diagram  of  a  peripheral  sensory  neurone. 


peripheral  nerve -trunks.  A  peripheral  sensory  neurone  may  there- 
fore be  diagramed  as  in  figure  134.  The  statement  was  made 
above  that  the  essential  portion  of  a  sensory  nerve-ending  is  a  telo- 
dendrion (end-brush)  or  several  telodendria  of  the  dendrite  of  a 
peripheral   sensory   neurone.      The  character  of  a  sensory   nerve- 


i68 


THE    TISSUES. 


ending  depends,  therefore,  on  the  complexity  of  this  end-brush  and 
on  its  relation  to  the  other  tissue  elements  which  take  part  in  the 
formation  of  the  sensory  nerve-endings.     Bearing  this  in  mind,  the 


Fig.  135. — Termination  of  sensory  nerve-fibers  in  the  mucosa  and  epithelium  of  the  ure- 
thra  of  cat;  methylene-blue  preparation  (Huber,  **  Jour.  Comp.  Neurol.,"  vol.  x). 

following  classification  of  such  nerve-endings  can  be  made  : 

I.  Free  Sensory  Nerve -endings. — In  these  the  telodendrion  is  not 


SENSORY    NERVE-ENDINGS.  1 69 

inclosed  in   an  investing   capsule  which  forms  a  structural  part  of 
the  ending. 

2.  Encapsulated  Endings. — In  which  the  telodendrion  or  several 
telodendria  are  surrounded  by  an  investing  capsule  which  separates 
them  more  or  less  completely  from  the  surrounding  tissue. 

1.  Free  sensory  nerve=endings  are  found  in  all  epithelial  tis- 
sues and  in  fibrous  connective  tissue  of  certain  regions.  A  sensory 
nerve-fiber  terminating  in  such  an  ending  usually  proceeds  without 
branching  to  near  its  place  of  termination,  where,  while  yet  a 
medullated  fiber,  it  branches  and  rebranches  a  number  of  times, 
always  at  the  nodes  of  Ranvier,  the  resultant  branches  diverging  at 
various  angles.  If  the  free  sensory  endings  are  in  epithelial  tissue, 
these  larger  medullated  branches  are  situated  in  tne  connective- 
tissue  mucosa  under  the  epithelium.  From  these  larger  medullated 
branches,  are  given  off  smaller  ones,  also  medullated,  which  may 
divide  further,  and  which  pass  up  toward  the  epithelium,  and  near  its 
under  surface  divide  into  nonmedullated  branches.  Nonmedullated 
branches  are  also  given  off  from  the  medullated  ones  as  they 
approach  the  epithelium,  leaving  the  parent  fibers  at  the  nodes  of 
Ranvier.  Many  of  the  nonmedullated  branches  thus  formed,  after 
coursing  a  variable  distance  under  the  epithelium,  enter  it  and  break 
up  into  numerous  very  small  branches,  which,  after  repeated  divi- 
sion, terminate  between  the  epithelial  cells  in  small  nodules  or 
discs  of  variable  size  and  configuration.  The  small  branches  result- 
ing from  a  division  of  one  of  the  larger  nonmedullated  branches 
constitute  one  of  the  terminal  telodendria  or  end-branches  of  the 
dendrites  of  peripheral  sensory  neurones  terminating  in  free  sensory 
nerve-endings.  In  fibrous  connective  tissue  the  same  general 
arrangement  of  the  branches  prevails.  In  figure  135  is  shown  the 
peripheral  distribution  of  the  dendrite  of  a  peripheral  sensory 
neurone  terminating  in  a  free  sensory  nerve-ending. 

2.  Encapsulated  Sensory  Nerve=endings. — These  nerve-end- 
ings may  be  divided  into  two  quite  distinct  groups, — such  as  have  a 
relatively  thin  fibrous-tissue  capsule, 

containing  mainly  telodendria  of  the 

nerve  or  nerves  terminating  therein,  ^ — ^ 

and  such  as  have  a  distinctly  lamel-  J0^^^^^^^^^^ 

lated,  fibrous  tissue  capsule,  usually  j^r^^^^^^^ 

investing,  besides   the  nerve-termi-  Ä^ä^^^^Mi  m 

nation,  other  tissue  elements.      To  IHjIt^^^^^^B 

the  former  group  belong  three  types  Iv^Ov^^^^^W  F 

of  sensory   nerve  -  endings,  which,  ^^^^^^^^Tm 

owing  to  their  similarity  of  struc-  ^^^^^^i^ 

ture,   may  be    described    together.  „.         ^      t-   , ,   ,.     r  t^ 

„,     '           ■'     ,             ,  1     11         c  -ß  Flg.    136. —  End-bulb  of   Krause 

Ihese  are  the  end-bulbs  Ol    Krause,  from  conjunctiva  of  man  ;   methylene- 

Meissner's     tactile    corpuscles,    and  blue   stain    (Dogiel,    "Arch.    f.    mik. 

the  genital  corpuscles.     They  have      '^"^^•'"  ^°^-  '^^^^^'")- 
all   been   investigated    recently  by 


I/o 


THE    TISSUES. 


Dogiel,   and  the  account  here   given  follows   closely   his  descrip- 
tion. 

End-biilbs  of  Krause. — Under  this  designation  there  are  described 
a  variety  of  endings  which  vary  slightly  in  size  and  shape.  They 
are  found  in  the  conjunctiva  and  edge  of  the  cornea,  in  the  lips  and 
lining  of  the  oral  cavity,  in  the  glans  penis  and  clitoris,  and  prob- 
ably also  in  other  parts  of  the  dermis.  In  form  they  are  round, 
oval,  or  pear-shaped.  Their  size  varies  from  0.02  to  0.03  mm. 
long  and  from  0.015  to  0.025  mm.  broad  for  the  smaller  ones, 
and  from  0.045  to  o.  10  mm.  long  and  from  0.02  to  0.08  mm. 
broad  for  the  larger  ones.  They  have  a  relatively  thin  capsule 
in  which  nuclei  are  quite  numerous.  One,  two,  or  three  medul- 
lated  nerves  go  to  each  end-bulb.  These  may  lose  their  medul- 
lary sheath  at  the  capsule  or  at  a  variable  distance  from  it.  The 
naked  axis-cylinders,  soon  after  entering  the  capsule,  divide  into  two, 
three,  or  four  branches,  which  form  several  circular  or  spiral  turns 
in  the  same  or  in  opposite  directions.  These  fibers  then  divide  into 
varicose  branches,  which  undergo  further  division,  the  resulting 
branches  interlacing  to  form  a  bundle  of  variously  tangled  fibers 
which  may  be  loosely  or  tightly  woven. 

Between  the  nerve-fibers  and  their  branches,  within  the  capsule, 

there  is  found  a  semifluid  sub- 
stance, which  is  granular  in  fixed 
preparations. 

Meissner  s  Corpuscles.  — These 
corpuscles  are  found  in  man  in 
the  subepidermal  connective  tissue 
of  the  hand  and  foot  and  outer 
surface  of  the  forearm,  in  the  nip- 
ple, border  of  the  eyelids,  lips, 
glans  penis  and  clitoris.  They  are 
most  numerous  in  the  palmar  sur- 
face of  the  distal  phalanx  of  the 
fingers.  They  are  oval  in  shape, 
sometimes  somewhat  irregular, 
and  vary  in  size,  being  from  45  // 
to  50  fi  broad  and  from  1 10  //.  to 
180^  long.  They  possess  a  thin 
connective-tissue  capsule,  in  which 
are  found  round  or  oval  nuclei, 
some  of  which  have  an  oblique 
position  to  the  axis  of  the  corpus- 
cle. One  meduUated  nerve  ends 
in  the  smaller  corpuscles,  two  or 
three  or  even  more  in  the  larger 
ones.  After  piercing  the  capsule, 
the  medullated  nerves  lose  their 
medullary  sheaths,   the    naked   axis-cylinders   making   a  variable 


Fig.  137. — Meissner' s  tactile  corpus- 
cle; methylene-blue  stain  (Dogiel,  "In- 
ternat. Monatsschr.  f.  Anat.  u.  Phys.," 
vol.  IX). 


SENSORY    NERVE-ENDINGS.  I/I 

number  of  circular  or  spiral  turns,  some  of  which  are  parallel,  others 
crossing  at  various  angles.  These  larger  branches  are  all  beset 
with  large,  spindle-shaped,  round,  or  pear-shaped  varicosities.  The 
larger  branches,  after  making  the  windings  mentioned,  break  up 
into  many  varicose  branches,  which  interlace  and  form  a  most  com- 
plex network.  One  usually  finds  one  or  several  larger  naked  axis- 
cylinders,  which  pass  up  through  .the  axis  of  the  spiral  of  fibers 
thus  formed  ;  these  give  off  branches  which  contribute  to  the  spiral 
formation. 

Genital  Corpuscles.— These  corpuscles  are  found  in  the  deeper 
part  of  the  mucosa  of  the  glans  penis  and  the  prepuce  of  the 
male  and  the  clitoris  and  neighboring  structures  of  the  female. 
Their    shape    varies;    thev  may    be    round,   oval,  egg-   or    pear- 


Fig     138  —Genital   corpuscle   from  the   glans   penis  of    man  ;    methylene-blue   stain 
(Dogiel,  "Arch.  f.  mik.  Anat.,"  vol.  XLI). 

shaped,  or  even  slightly  lobulated.  Their  size  varies  from  0.04 
to  o.  10'  mm.  in  breadth  and  from  0.06  to  0.40  mm.  in  length.  They 
are  surrounded  by  a  relatively  thick  fibrous  capsule,  consistmg 
of  from  three  to  eight  quite  distinct  lamellae,  between  which  irregu- 
lar flattened  cells  with  round  or  oval  nuclei  are  found.  Within 
this  capsule,  there  is  found  a  core,  which  seems  to  consist  of  a  semi- 
fluid substance,  slightly  granular  in  fixed  preparations,  the  nature 
of  which  is  not  fully  known.  The  number  of  sensory  nerves  gomg 
to  each  corpuscle  varies  from  one  to  two  for  the  smaller  ones,  and 
from  eight  to  ten  for  the  larger  corpuscles.  The  medullated  nerves, 
after  entering  the  corpuscle,  divide  dichotomously,  the  resultant 
branches  assuming  a  circular  or  spiral  course,  and  interlacing  m 
various  ways,  within  the  capsule.    After  a  few  turns,  the  medullated 


1/2 


THE    TISSUES. 


branches  lose  their  medullary  sheaths  and  undergo  further  di- 
vision, often  dividing  repeatedly.  The  nonmedullated  nerves  re- 
sulting from  these  divisions,  the  majority  of  which  are  varicose, 
form  a  most  complicated  network,  the  whole  nerve  network  pre- 
senting a  structure  which  resembles  a  tangle  of  fine  threads. 
In  the  meshes  of  this  network  is  found  the  semifluid  substance 
of  the  core.  Now  and  then  some  of  the  larger  fibers  of  the 
network  leave  the  corpuscle  and  terminate  in  neighboring  cor- 
puscles, or  pass  to  the  epithelium,  where  they  end  between  the 
cells. 

These  three  sensory  nerve-endings  —  end-bulbs  of  Krause, 
Meissner's  tactile  corpuscles,  genital  corpuscles — are,  as  Dogiel  has 
stated,  very  similar  in  structure.  Each  has  a  thin  connective-tissue 
capsule,  surrounding  a  core,  consisting  of  a  semifluid  substance, 
concerning  which  our  knowledge  is  as  yet  imperfect.  One  or  sev- 
eral medullated  nerves  go  to  each  corpuscle,  which,  after  losing 
their  medullary  sheaths,  divide  and  subdivide  into  numerous  fine 
varicose  branches,  which  are  variously  interwoven,  forming  a  more 
or  less  dense  plexus  of  interlacing  and,  according  to  Dogiel,  anas- 
tomosing fibers.  The  chief  differences  are  those  of  form  and  size, 
and  of  position  with  reference  to  the  epithelium.  Of  the  three  forms 
of  endings,  the  genital  corpuscle  is  the  largest,  and  occupies  the  deep- 
est position  in  the  subepithelial  connective  tissue  ;  Meissner's  cor- 
puscle is  intermediate  in  size,  and  is  found  immediately  under  the 
epithelium  ;  while  the  end-bulbs  of  Krause  are  the  smallest  of  these 


Fig.  139. — Cylindric  end-bulb  of  Krause  from  intermuscular  fibrous  tissue  septum  of  cat; 

methylene-blue  stain. 


three  forms  of  sensory  endings  and  may  be  found  in  the  papillae  or 
in  the  deeper  connective  tissue. 

A  somewhat  smaller  nerve-ending  of  long,  oval,  or  cylindric 
form,  known  as  the  cylindric  end-bidb  of  Krause,  is  found  in  various 
parts  of  the  skin  and  oral  mucous  membrane,  in  striated  muscle 
and  in  tendinous  tissue.  These  corpuscles  consist  of  a  thin  nucle- 
ated capsule,  investing  a  semifluid  core.  The  nerve-fiber,  after 
losing  its  medullary  sheath  and  fibrous  sheath  (the  latter  becomes 
continuous  with  the  capsule),  passes  through  the  core,  generally 
without  branching,  as  a  naked  axis-cylinder,  terminating  at  its  end, 
usually  in  a  small  bulb.      (Fig.  139.) 

The  majority  of  the  sensory  nerve-endings  with  well-developed 


SENSORY    NERVE-ENDINGS. 


173 


lamellated  capsules  are  relatively  large  structures.  We  shall  con- 
sider especially  the  Vater-Pacinian  corpuscles,  the  neuromuscular 
end-organs,  and  the  neurotendinous  end-organs. 

Vater- Pacinia7i  Corpuscles. — These  corpuscles  are  of  oval  shape 
and  vary  much  in  size,  the  largest  being  about  o.io  of  an 
inch  long  and  0.04  of  an  inch  broad.  The  greater  portion  of  the 
corpuscle  is  made  up  of  a  series  of  concentric  lamellae,  varying 
in  number  from  twenty  to  sixty.     These   lamellae  are  made  up  of 


'■»  '-'  'Vfir'^  ^   " 


Fig.  140. — Vater-Pacinian  corpuscle  from  the  mesentery  of  a  cat;  X  45-  The 
figure  shows  a  general  view  of  the  corpuscle,  a.  Axis-cylinder  in  the  core  ;  ik,  core  ; 
mn,  medullated  nerve-fibers  entering  the  core  ("  Atlas  and  Epitome  of  Human  His- 
tology,"  Sobotta). 

white  fibrous  tissue  fibers,  rather  loosely  woven,  between  which  is 
found  a  small  amount  of  lymph,  containing  usually  a  few  leucocytes. 
The  lamellae  are  covered  on  both  surfaces  by  a  layer  of  endothelial 
cells  (Schwalbe).  Between  two  consecutive  lamellae  there  is  found  an 
interlamellar  space,  also  containing  lymph.  The  axis  of  the  cor- 
puscle is  occupied  by  a  core,  consisting  of  a  semifluid,  granular 
substance,  in  the  periphery  of  which  oval  nuclei  are  said  to  be 
found.  Usually  one  large  medullated  nerve-fiber  goes  to  each  cor- 
puscle. The  fibrous  tissue  sheath  of  this  nerve-fiber  becomes  con- 
tinuous with  the  outer  lamellae  of  the  capsule.  The  medullary 
sheath  accompanies  the  axis-cylinder  through  the  concentric  lamel- 
lae until  the  core  is  reached,  where  it  disappears.  The  naked  axis- 
cylinder  usually  passes  through  the  core  to  its  distal  end,  where  it 
divides  into  three,  four,  or  five  branches  which  terminate  in  large, 
irregular  end-discs.  The  axis-cylinder  may,  however,  divide  soon 
after  it  enters  the  core  into  two  or  three  or  even  four  branches, 
these  passing  to  the  distal  end  of  the  core  before  terminating  in  the 
end-discs  above  mentioned.  Both  Retzius  and  Sala  state  that  the 
naked  axis-cylinders,  after  entering  the  core,  give  off  numerous  short 
side  branches,  terminating  in  small  knobs,  which  remind  these  ob- 
servers of  the  fine  side  branches  or  thorns  seen  on  the  dendrites  of 
Purkinje's  cells  and  of  the  pyramidal  cells  of  the  cortex,  when  stained 


174 


THE    TISSUES. 


after  the  Golgi  method.  In  company  with  the  large  nerve -fibers  here 
mentioned,  Sala  has  described  other  nerve-fibers,  quite  independent 
of  them  and  much  finer,  which  after  entering  the  corpuscle  divide 
repeatedly,  the  resulting  fibers  forming  a  plexus  around  the  central 
fiber.  A  small  arteriole  enters  the  corpuscle  with  the  nerve-fiber, 
dividing  into  capillary  branches  found  between  the  lamellae  of 
the  capsule. 

The  Vater- Pacinian  corpuscles  have  a  wide  distribution.  They 
are  numerous  in  the  deeper  parts  of  the  dermis  of  the  hand  and 
foot,  and  also  near  the  joints,  especially  on  the  flexor  side.  They 
have  been  found  in  the  periosteum  of  certain  bones  and  in  tendons 
and  intermuscular  septa,  and  even  in  muscles.  They  are  further 
found  in  the  epineurial  sheaths  of  certain  nerve-trunks  and  near 


Fig.  141. — Pacinian  corpuscles  from  mesorectum  of  kitten  :  A,  Showing  the  fine 
liranches  on  central  nerve-fiber ;  B,  the  network  of  fine  nerve-fibers  about  the  central 
fiber;  methylene-blue  preparation  (Sala,  "Anat.  Anzeiger,"  vol  xvi). 


large  vessels.  They  are  numerous  in  the  peritoneum  and  mesentery, 
pleura  and  pericardium.  In  the  mesentery  of  the  cat,  where  these 
nerve-endings  are  large  and  numerous,  they  are  readily  seen  with  the 
unaided  eye  as  small,  pearly  bodies. 

In  the  bill  and  tongue  of  water  birds,  especially  of  the  duck,  are 
found  nerve-endings,  known  as  the  corpuscles  of  Herbst,  which  re- 
semble the  Vater- Pacinian  corpuscles  ;  they  differ  from  the  latter  in 
having  cubic  cells  in  the  core.     (Fig.   142.) 

Neuromuscular  Nerve  End-organs. — These  nerve  end-organs 
consist  of  a  small  bundle  of  muscle-fibers,  surrounded  by  an  invest- 


SENSORY    NERVE-ENDINGS. 


175 


ing  capsule,  within  which  one  or  several  sensory  nerves  terminate. 
They  are  spindle-shaped  structures  varying  in  length  from  0.75  to  4 
mm.,  and  in  breadth,  where  widest,  from  80  to  200  //  (Sherrington, 
94).  In  them  there  is  recognized  a  proximal  polar  region,  an 
equatorial  region,  and  a  distal  polar  region.  The  muscle-fibers  of 
this  nerve-ending,  known  as  the  intrafusal  fibers,  which  may  vary  in 
number  from  3  or  4  to  20  or  even  more,  are  much  smaller  than  the 
ordinary  voluntary  muscle-fibers  and  differ  from  them  structur- 
ally, and  result  from  a  division  of  one  or  several  muscle-fibers  of 
the  red  variety.  In  the  proximal  polar  region  the  intrafusal  fibers 
present  an  appearance  which  is  similar  to  that  of  voluntary  muscle- 
fibers  of  the  red  variety  ;  in  the  equatorial  region  they  possess  rela- 


-  Nucleus  of  lamellae. 


End-cell  of  core. 
Lamellae. 

Axis-cylinder  in  core. 
Cubic  cells  of  core. 

Termination  of  medul- 
lary sheath. 


Axis-cylinder  of 
nerve-fiber. 

Medullary  sheath  of 

ner\-e-fiber. 
Neurilemma  and  sheath 

of  Henle. 


Fig.  142. — Corpuscle  of  Herbst  from  bill  of  duck;  X  600. 


tively  few  muscle- fibrils  and  are  rich  in  sarcoplasm  and  the  muscle- 
nuclei  are  numerous  ;  the  striation  is  here  indistinct.  In  the  distal 
polar  region  the  intrafusal  fibers  are  again  more  distinctly  striated 
and,  a  short  distance  beyond  the  end-organ,  become  greatly  reduced 
in  size,  and  terminate  as  very  small  fibers,  still  showing,  however,  a 
cross-striation.  In  figure  143  is  shown  a  single  intrafusal  muscle- 
fiber.  Owing  to  the  length  of  such  a  fiber  it  was  necessary  to  rep- 
resent it  in  several  segments. 

The  intrafusal  muscle-fibers  are  surrounded  by  a  capsule  con- 
sisting of  from  four  to  eight  concentric  layers  of  white  fibrous  tissue. 
At  the  proximal  end  this  capsule  is  continuous  with  the  connective 


1/6 


THE     TISSUES. 


tissue  found  between  the  muscle-fibers — endo-  and  perimysium.  It 
attains  its  greatest  diameter  in  the  equatorial  region  of  the  nerve 
end-organ,  and  becomes  narrower  again  at  its  distal  end,  where  it 
may  end  in  tendon  or  become  continuous  with  the  connective  tissue 


Fig.  143. — Intrafusal  muscle-fiber  from  neuromuscular  nerve  end-organ  of  rabbit : 
A,  From  proximal  polar  region ;  B,  equatorial  region  ;   C,  distal  polar  region. 

of  the  muscle.  Immediately  surrounding  the  intrafusal  fibers  is  found 
another  connective -tissue  sheath  known  as  the  axial  sheath,  and 
between  this  and  the  capsule  there  is  found  a  lymph-space  bridged 
over  by  trabeculae  of  fibrous  tissue,  to  which  the  name  periaxial 
lymph-space  has  been  given.   (Fig.  144.) 

By  degenerating  the  motor  nerves  going  to  a  muscle,  Sherrington 


Q^  )**« 


Fig.  144. — Cross-section  of  a  neuromuscular  nerve  end-organ  from  interosseous  (foot) 
muscle  of  man  ;  fixed  in  formalin  and  stained  in  hematoxylin  and  eosin. 


determined  that  the  nerve-fibers  ending  in  the  neuromuscular  nerve 
end-organs  were  sensory  in  character.  The  manner  of  termination  in 
these  end-organs  of  the  nerve-fibers  ending  therein  has  been  studied 
by  Kerschner,   KöUiker,  Ruffini,  Ruber  and  De  Witt,  Dogiel,  and 


SENSORY    NERVE-ENDINGS.  177 

Others.      One  or  several  (three  or  four)  large  medullated  nerves,  sur- 
rounded by  a  sheath  of  Henle,  terminate  in  each  neuromuscular  end- 


Fig.  145. — Neuromuscular  nerve  end-organ  from  the  intrinsic  plantar  muscles  of 
dog  ;  from  teased  preparation  of  tissue  stained  in  methylene-blue.  The  figure  shows  the 
intrafusal  muscle-fibers,  the  nerve-fibers  and  their  terminations  ;  the  capsule  and  the  sheath 
of  Henle  are  not  shown  (Huber  and  DeWitt,  "Jour.  Comp.  Neurol.,"  vol.  VII). 

organ.     As  these  nerves   enter  the  capsule,  the  sheath    of  Henle 
blends   with  the   capsule.      The  medullated  nerve-fibers   now  and 
12 


178 


THE     TISSUES. 


then  divide  before  reaching  the  nerve  end-organs,  and  divide  several 
times  as  they  pass  through  the  capsule,  periaxial  space,  and  axial 
sheath.      Within  the  axial  sheath,  the  medullary  sheath  is  lost,  and 

the  naked  axis-cylinders  terminate  in 
one  or  several  ribbon  -  like  branches 
which  are  wound  circularly  or  spirally 
about  the  intrafusal  fibers  {animlospiral 
ending)  or  they  may  terminate  in  a 
number  of  larger  branches  which  again 
divide,  these  ending  in  irregular,  round, 
oval,  or  pear-shaped  discs  {^flower-like 
endings),  which  are  also  on  the  intra- 
fusal fibers.  These  flower-like  endings 
are  usually  at  the  ends  of  the  annulo- 
spiral  fibers.  In  the  smaller  end- 
organs  only  one  area  of  nerve-termi- 
nation has  been  observed  ;  in  the 
larger,  two,  three,  or  even  four  such 
areas  may  be  found. 

Neuromuscular  nerve  end-organs 
are  found  in  nearly  all  skeletal  muscles 
(not  in  the  extrinsic  eye  muscles  nor 
in  the  intrinsic  muscles  of  the  tongue), 
but  they  are  especially  numerous  in 
the  small  muscles  of  the  hand  and  foot. 
They  are  found  in  amphibia,  reptilia, 
birds,  and  mammalia,  presenting  the 
same  general  structure,  although  the 
ultimate  termination  of  the  nerve-fibers 
varies  somewhat  in  the  different  classes 
of  vertebrates. 

Neurotendinous  Nerve  End -organ 
(Golgi  Tendon  Spindle).  —  In  i88a 
Golgi  drew  attention  to  a  new  nerve 
end-organ  found  in  tendon,  describing 
quite  fully  its  general  structure  and 
less  fully  the  nerve  termination  found 
therein.  These  nerve  end-organs  are 
spindle  -  shaped  structures,  which  in 
man  vary  in  length  from  1.28  mm.  to 
1.42  mm.,  and  in  breadth  from  0.17 
mm.  to  0.25  mm.  (Köüiker).  Ciaccio 
mentions  a  neurotendinous  nerve  end- 
organ  found  in  a  woman,  which  was  2 
Fig.    146.  -  Neurotendinous      or  3  mm.  long.  A  capsule  consisting  of 

nerve  end-organ  from  rabbit;  teased       from  2  tO  6  fibrOUS    tisSUe  lamellae,  and 

preparation   of    tissue   stained  in      broadest  at  the  equatorial  part  of  the 

methylene-blue  ( Hube  rand  De  Witt,  ^  u  r- 

"Jour.  Comp.  Neurol.,"  vol.  x).         end-organ,  surrounds  a  number  oi  m- 


SENSORY    NERVE-ENDINGS. 


179 


trafusal  tendon  fasciculi.  The  capsule  is  continuous  at  the  prox- 
imal and  distal  ends  of  the  end-organ  with  the  internal  periten- 
dineum of  the  tendon  in  which  it  is  found.  The  number  of  the 
intrafusal  tendon  fasciculi  varies  from  eight  to  fifteen  or  even  more. 
They  are  smaller  than  the  ordinary  tendon  fasciculi,  from  which 
they  originate  by  division,  and  structurally  resemble  embryonic 
tendon,  in  that  they  stain  more  deeply  and  present  many  more 
nuclei  than  fully  developed  tendon.  The  intrafusal  tendon  fasciculi 
are  surrounded  by  an  axial  sheath  of  fibrous  tissue,  between  which 
and  the  capsule  there  is  found  a  periaxial  lymph-space. 


F'g-  ^47- — Cross-section  of  neurotendinous  nerve  end-organ  of  rabbit ;  from  tissue 
stained  in  methylene-blue  :  ;«,  Muscle-fibers  ;  /,  tendon  ;  c,  capsule  of  neurotendinous 
end-organ  ;  7nn,  medullated  nerve-fiber  (Huber  and  DeWitt,  "Jour,  of  Comp.  Neurol.," 
vol.  X). 

The  termination  of  the  nerve-fibers  ending  in  these  end-organs 
has  been  studied  by  Golgi,  Cattaneo,  Kerschner,  KöUiker,  Pansini, 
Ciaccio,  Huber  and  DeWitt.  One,  two,  or  three  large  medullated 
nerve-fibers,  surrounded  by  a  sheath  of  Henle,  end  in  each  end- 
organ  ;  as-  they  pass  through  the  capsule,  the  sheath  of  Henle 
blends  with  the  capsule.  The  medullated  nerve-fibers  before  enter- 
ing the  capsule  usually  branch  several  times,  branching  further 
within  the  capsule  and  axial  sheath.  Before  the  resultant  branches 
terminate  on  the  intrafusal  tendon  fasciculi,  the  medullarv  sheath  is 


1 80  THE    TISSUES. 

lost,  the  naked  axis-cylinder  further  dividing  into  two,  three,  or  four 
branches,  each  of  which  runs  along  on  the  intrafusal  fasciculi,  giving 
off  numerous  short,  irregular  side  branches,  which  partly  enclasp 
the  tendon  fasciculi  and  end  in  irregular  end-discs.  Some  of  the  ter- 
minal branches  pass  between  the  smaller  fibrous  tissue  bundles  of 
the  fasciculi,  ending  between  them. 

In  these  end-organs,  the  larger  nerve-branches  are  found  near 
the  center  of  the  bundle  of  intrafusal  tendon  fasciculi,  the  terminal 
branches  and  the  end-discs  nearer  their  periphery.  The  neuroten- 
dinous nerve  end-organs  are  widely  distributed,  being  found  in  all 
tendons  although  not  equally  numerous  in  all.  Like  the  neuromus- 
cular nerve  end-organs,  they  are  especially  numerous  in  the  small 
tendons  of  the  hand  and  foot.  Sensory  nerve  end-organs,  which 
resemble  in  structure  the  neurotendinous  end-organs  here  described, 
though  somewhat  smaller  than  these,  have  been  found  in  the  tendons 
of  the  extrinsic  eye-muscles. 

In  this  brief  account  of  the  mode  of  ending  of  the  telodendria  of 
the  dendrites  of  peripheral  sensory  neurones  (sensoiy  nerve-fibers) 
it  has  not  been  possible  to  discuss  any  but  the  more  typical  varie- 
ties of  sensory  nerve-endings.  Other  nerve -endings  will  be  consid- 
ered in  connection  with  the  several  organs  to  be  treated  later.  For 
a  fuller  discussion  of  this  subject,  the  reader  is  referred  to  special 
works  and  monographs. 

TECHNIC. 

Fresh  medullated  nerve-fibers,  when  teased  in  an  indifferent  fluid, 
show  the  peculiar  luster  of  the  medullary  sheath,  and  also  the 
nodes  of  Ranvier,  the  neurilemma  with  its  nuclei,  and  the  segments 
of  Lantermann.  At  the  cut  ends  of  the  fibers,  the  typical  coagula- 
tion of  their  medullary  portions  is  seen  in  the  form  of  drops  of  myelin. 
All  these  structures  can  also  be  seen  after  using  i  %  osmic  acid.  A  nerve 
(not  too  thick)  is  placed  in  a  i  ^  aqueous  osmic  acid  solution,  then 
washed  for  a  few  hours  in  distilled  water,  and  finally  carried  over  into 
absolute  alcohol.  After  dehydration,  small  pieces  are  cleared  with  oil  of 
cloves  and  the  fibers  teased  apart  upon  a  slide.  The  medullary  sheath  is 
stained  black  and  hides  the  axial  space,  the  nodes  are  clear,  the  neu- 
rilemma is  sometimes  seen  as  a  light  membrane,  and  the  nuclei  of  the 
fibers  are  of  a  lenticular  shape,  and  stained  brown. 

The  nodes  of  Ranvier  may  also  be  demonstrated  by  means  of 
silver  nitrate  solution.  Fresh  nerve-fibers  are  either  teased  in  distilled 
water  to  which  a  trace  of  1%  silver  nitrate  solution  has  been  added  (the 
nodes  of  Ranvier  appear  after  a  short  time  as  small  crosses),  or  whole 
nerves  are  placed  for  twenty-four  hours  in  a  0.5%  aqueous  solution 
of  silver  nitrate,  washed  for  a  short  time  with  water,  hardened  in 
alcohol,  after  which  they  are  imbedded  in  paraffin  and  cut  longitudinally. 
Exposure  to  light  will  soon  bring  out  the  ' '  crosses  of  Ranvier  ' '  at  the 
nodes.  The  appearance  of  these  crosses  is  due  to  the  fact  that  the 
silver  nitrate  solution  first  penetrates  at  the  nodes  of  Ranvier,  and  then 
passes  by  capillary  attraction  along  the  axial  cord  for  some  distance. 
After  the  reduction  of  the  silver,  the  cruciform  figures  appear  colored 


THE    NERVOUS    TISSUES. 


i8i 


black.  Occasionally,  a  peculiar  transverse  striation  is  seen  in  the  longi- 
tudinal portions  of  the  crosses.  These  are  known  as  Frommann's  lines. 
Their  origin  and  significance  have  not  as  yet  been  satisfactorily  ex- 
plained. 

To  demonstrate  the  fibrils  of  the  axial  cord  a  piece  of  a  small 
nerve  is  stretched  on  a  match  or  toothpick  and  fixed  for  four  hours  in  a 
0.5%  osmic  acid  solution,  after  which  it  is  washed  in  water  for  the  same 
length  of  time  and  immersed  in  90^  alcohol  for  twenty-four  hours.  The 
preparation  is  now  stained  for  another  twenty-four  hours  in  a  saturated 
aqueous  solution  of  fuchsin  S  and 
then  placed  for  three  days  in  abso- 
lute alcohol.  Finally,  the  nerve  is 
passed  as  rapidly  as  possible  through 
toluol,  toluol-paraffin,  and  then  im- 
bedded in  paraffin.  The  proper 
orientation  of  the  specimen  is  of  the 
greatest  importance,  as  is  also  the 
cutting  of  thin  sections.  In  a  lon- 
gitudinal section  red  fibrils  of  almost 
uniform  thickness  and  evenly  dis- 
tributed throughout  the  axial  space 
are  seen  lying  in  the  colorless  neuro- 


Medullary 
sheath. 


Axis-cylin- 
der. 


Fig.  148. — Ranvier's  crosses  from  sci- 
atic nerve  of  rabbit  treated  with  silver  ni- 
trate solution ;  X  120.  Frommann's  lines 
can  be  seen  in  a  few  fibers. 


■  Fig.  149.  —  Medullated  nerve-fiber 
from  sciatic  nerve  of  frog.  In  two  places 
the  medullary  sheath  has  been  pulled 
away  by  teasing,  showing  the  *' naked 
axis-cylinder"  ;  X  212. 


plasm,  and  parallel  to  the  long  axis  of  the  nerve-fiber.  In  cross-section 
the  axial  fibrils  appear  as  evenly  distributed  dots.  Attention  must  be 
called  to  the  fact  that  the  fibrils  are  not  equally  well  stained  in  all  cases 
(Kupffer,  83,  II ;  compare  also  Jacobi  and  Joseph). 

When  the  fiber  is  less  carefully  treated,  the  fibrils  fuse  with  the 
neuroplasm  to  form  the  ''axis-cylinder"  of  authors.  As  the  appearance 
of  the  latter  is  due  to  a  shrinkage  of  the  contents  of  the  axial  space,  it  is 
easy  to  understand  that  one  reagent  may  have  a  greater  effect  in  this  re- 
spect than  another.  The  thinnest  axis-cylinders  are  produced  by  chromic 
acid  and  its  salts,  while  thicker  ones  are  seen  in  nerve-fibers  fixed  in 
alcohol.     These  variations  are  best  seen  in  cross-sections,  in  which  the 


182 


THE    TISSUES. 


Dendrite. 


axis-cylinders  sometimes  appear  as  round  dots  and  again  as  stellate  figures. 
The  latter  are  due  to  pressure  on  the  shrinking  axial  cord  by  the  unevenly 
coagulated  medullary  sheath.  As  the  medullary  sheath  in  such  prepara- 
tions crumbles  away  in  many  places,  large  areas  of  the  axis-cylinder  may 
often  be  isolated  by  teasing  (Fig.  149). 

Sensory  and  motor  nerve-endings  may  be  stained  after  gold  chlorid 
and  chrome-silver  methods  (see  methods  of  impregnation,  page  47),  or 
after  the  intra  vttatn  methylene -blue  method  suggested  by  Ehrlich  and 
variously  modified  by  other  investigators. 

If  freshly  teased  fibers  be  treated  with  glacial  acetic  acid,  the 
axis-cylinders  swell  up  and  issue  from  the  ends  of  the  fibers  in  irregular 
masses  showing  fine  longitudinal  striation  (Kölliker,  93).  The  structures 
of  the  axial  space  dissolve  in  i^  hydrochloric  acid,  as  well  as  in  a  lo'fo 
solution  of  sodium  chlorid  (Halliburton). 

For  the  isolation  of  ganglion  cells,  33'^  alcohol,  o.i  to  0.5^ 
chromic  acid,  or  i^   solution  of  potassium  bichromate  may  be  used. 

Small  pieces  of  the  spinal 
cord  and  brain  containing 
ganglion  cells  are  treated 
with  a  small  quantity  of 
one  of  the  above  solutions 
for  one  or  two  weeks.  After 
this  interval  the  prepara- 
tions may  be  teased  and 
the  isolated  ganglion  cells 
stained  on  a  slide  and 
mounted  in  glycerin.  They 
may  even  be  fixed  in  situ 
by  injecting  a  i  %  solution 
of  osmic  acid  or  33^  al- 
cohol into  the  areas  of 
the  brain  or  spinal  cord 
containing  ganglion  cells. 
The  region  thus  treated  is 
then  cut  out  and  teased. 

The  nonmedullated  or 
"Remak's  fibers"  are  ob- 
tained by  teasing  a  sym- 
pathetic nerve,  or,  better, 
a  piece  of  the  vagus  pre- 
viously treated  with  osmic 
acid.  Between  the  black- 
ened medullated  fibers  of 
the  pneumogastric  are  seen  numerous  unstained  fibers  of  Remak. 

The  fibers  of  the  olfactory  nerve  are  stained  brown  by  osmic  acid. 

Ehrlich 's  methylene-blue  method  consists  in  an  intra  vitam 
staining  of  ganglion  cells,  nerve-fibers,  and  nerve-endings.  The  method 
is  much  more  applicable  to  the  staining  of  peripheral  ganglia  (spinal  and 
sympathetic  ganglia),  peripheral  nerves,  and  nerve-endings  than  to  stain- 
ing the  elements  of  the  central  nervous  system,  although  the  latter  may 
also  be  stained  by  means  of  this  method. 

Two  methods  for  bringing  the  stain  in  contact  with  the  nerve-tissues 
are  now  in  use  :  (i)  injecting  the  methylene-blue  solution  into  the  living 


-    Neuraxis. 


Fig.  150. — A  ganglion  cell  from  anterior  horn 
of  the  spinal  cord  of  calf ;  teased  preparation  ; 
X  140.  By  this  method  only  the  coarsest  ramifica- 
tions of  the  dendrites  are  preserved ;  the  rest  are 
torn  off. 


THE    NERVOUS    TISSUES.  1 83 

tissues  through  the  blood-vessels  ;  (2)  adding  a  few  drops  of  the  stain  to 
small  pieces  of  perfectly  fresh  tissues  removed  from  the  body.  The  solu- 
tion used  for  injecting  the  tissues  is  prepared  as  follows  :  i  gm.  of  methyl- 
ene-blue^  is  mixed  in  a  small  flask  with  100  c.c.  of  normal  salt  solution 
and  heated  over  a  flame  until  the  solution  becomes  hot.  It  is  then  allowed 
to  cool ;  when  filtered,  it  is  ready  for  use.  A  cannula  is  tied  into  the 
main  artery  of  the  part  in  which  it  is  desired  to  stain  the  nerve  elements, 
and  sufficient  of  the  foregoing  methylene -blue  solution  injected  to  give 
the  part  a  decidedly  blue  color.  After  the  injection  the  part  to  be 
studied  remains  undisturbed  for  about  one -half  hour,  after  which  time 
small,  or  at  least  thin,  pieces  of  the  tissue  to  be  studied  are  removed  to  a 
slide  moistened  in  normal  salt  solution,  and  exposed  to  the  air.  The 
tissues  remain  on  the  slide  until  the  nerve-cells,  nerve-fibers,  or  nerve- 
endings  seem  satisfactorily  stained.  After  placing  the  tissues  on  the  slide, 
they  are  examined  under  the  microscope  (without  covering  with  a  cover- 
glass)  every  two  or  three  minutes,  until  such  examination  shows  blue 
color  in  the  neuraxes  of  the  nerve-fibers  and  their  terminations,  or  in  the 
nerve-cells,  if  there  be  any  in  the  tissues  examined.  Care  should  be 
taken  not  to  miss  the  time  when  the  staining  has  reached  its  full  develop- 
ment, as  the  blue  color  usually  fades  again  and  only  inferior  preparations 

are  obtained. 

Tissues  thus  stained  may  be  fixed  by  one  of  two  methods  (or  modifi- 
cations of  these  methods),  the  selection  of  the  method  depending  some- 
what on  the  results  desired.  If  it  is  desired  to  gain  preparations  giving 
the  general  course  of  nerves,  the  formation  of  nerve-plexuses,  the  relations 
of  afferent  and  efferent  nerves  to  the  nerve-cells  in  ganglia,  or  the  gen- 
eral arrangement  of  the  terminal  branches  of  nerve -fibers  in  nerve  end- 
organs,  the  tissues  are  placed  in  a  saturated  aqueous  solution  of  ammo- 
nium picrate  (Dogiel)  in  which  the  blue  color  of  the  tissues  is  in  a  short 
time  changed  to  a  purplish  color.  In  this  solution  the  tissues  remain  for 
from  twelve  to  twenty-four  hours,  and  are  then  transferred  to  a  mixture 
consisting  of  equal  parts  of  a  saturated  aqueous  solution  of  ammonium 
picrate  and  glycerin,  in  which  they  remain  another  twenty-four  hours  ; 
they  may,  however,  without  detriment  remain  in  the  mixture  several 
days.     The  tissues  are  then  mounted  in  this  ammonium  picrate-glycenn 

mixture.  .  . 

If,  on  the  other  hand,  it  is  desired  to  section  tissues  stained  intra 
vitamin  methylene-blue,  the  following  method,  slightly  modified  from 
that  given  by  Bethe,  is  suggested.  The  following  fixative  is  prepared : 
Ammonium  molybdate,  i  gm.;  distilled  water,  10  c.c;  hydrochloric 
acid,  I  drop.  The  solution  is  prepared  by  grinding  the  ammonium 
molybdate  to  a  fine  powder,  removing  it  to  a  flask,  and  adding  the 
required  quantity  of  water.  The  flask  is  now  heated  until  the  ammonium 
molybdate  is  entirely  dissolved,  when  the  hydrochloric  acid  is  added. 
Before  using  this  fixative  it  is  necessary  to  cool  it  to  2°-5°  C.  It  is,  there- 
fore, well  to  prepare  it  before  the  injection  is  made,  and  surround  it  with 
an  ice  mixture.  In  this  fixative  the  tissues  remain  for  from  twelve  to 
twenty-four  hours.  After  the  first  six  to  eight  hours  it  is  not  necessary  to 
keep  the  fixative  below  ordinary  room-temperature.  After  fixation  the 
tissues  are  washed  for  an  hour  in  distilled  water.  They  are  then  hard- 
ened and  dehydrated  in  absolute  alcohol.  It  is  advisable  to  hasten  this 
step  as  much  as  possible,  though  not  at  the  risk  of  imperfect  dehydration. 

1  Methylenblau,  rectificiert  nach  Ehrlich,  Grübler,  Leipzig. 


184  THE    TISSUES. 

The  tissues  are  then  transferred  to  xylol  and  imbedded  in  parafifin,  sec- 
tioned, fixed  to  the  slide  or  cover-glass  with  albumin  fixative,  and  may 
be  double  stained  in  alum-carmin  or  alum -cochineal.  After  staining  in 
either  of  these  stains,  the  sections  are  thoroughly  dehydrated  and  cleared 
in  oil  ofbergamot.  The  oil  is  washed  off  with  xylol  and  the  sections  are 
mounted  in  Canada  balsam. 

In  staining  nerve-fibers  with  methylene-blue  by  local  application 
of  the  stain  to  the  tissues,  the  tissues  to  be  studied  are  removed  from  an 
animal  which  has  just  been  killed,  divided  in  small  pieces,  and  placed  on 
a  slide  moistened  with  normal  salt  solution.  A  few  drops  of  a  -2^%  to 
■Y^'^o  solution  of  methylene-blue  in  normal  salt  solution  are  added  from 
time  to  time — sufficient  to  keep  the  tissues  moistened  by  the  solution,  but 
not  enough  to  cover  them.  The  preparations  are  examined  from  time  to 
time,  under  the  microscope,  to  see  whether  the  nerve  elements  are  stained. 
The  length  of  time  required  for  staining  by  this  method  varies.  Some- 
times the  nerve  elements  are  stained  in  half  an  hour ;  again,  it  may  re- 
quire two  and  one-half  hours  ;  on  an  average,  about  one  hour.  As  soon 
as  the  tissues  seem  well  stained  they  are  fixed  as  previously  directed. 
Dogiel  has  found  that  sympathetic  ganglia  and  sensory  nerve-fibers  of  the 
heart  removed  from  the  human  body  several  hours  after  death  may  be 
stained  by  means  of  the  foregoing  method. 

In  order  to  obviate  the  necessity  for  the  low  temperature  of  the  pre- 
vious method,  Bethe  (96)  has  recommended  the  following  procedure  : 
According  to  the  method  of  Smirnow  and  Dogiel,  he  first  employs  as  a 
preliminary  fixing  agent  a  concentrated  aqueous  solution  of  ammonium 
picrate.  In  this  he  places  the  tissue,  previously  treated  with  methylene - 
iDlue,  for  from  ten  to  fifteen  minutes.  Without  further  washing  the  larger 
objects  are  immersed  in  a  mixture  composed  of  ammonium  molybdate 
(or  sodium  phosphomolybdate)  i  gm.,  distilled  water  20  c.c,  and  pure 
hydrochloric  acid  i  drop.  The  following  mixtures  may  also  be  employed 
for  the  same  purpose  :  ammonium  molybdate  (or  sodium  phosphomo- 
lybdate) I  gm.,  distilled  water  10  c.c,  2^  solution  of  chromic  acid 
10  c.c,  and  hydrochloric  acid  i  drop  ;  or,  for  very  thin  gross  specimens 
or  sections,  ammonium  molybdate  (or  sodium  phosphomolybdate)  i  gm., 
distilled  water,  10  c.c,  0.5^  osmic  acid  10  c.c,  and  hydrochloric  acid 
I  drop.  Small  objects  are  permitted  to  remain  no  longer  than  from  three 
quarters  of  an  hour  to  one  hour  in  either  of  the  first  two  mixtures,  and 
not  more  than  from  four  to  twelve  hours  in  the  third.  After  fixing,  the 
specimens  are  washed  with  water,  carried  over  into  alcohol,  then  into  xylol, 
and  finally  imbedded  in  paraffin.  Subsequent  staining  with  alum-carmin, 
alum -cochineal,  or  one  of  the  neutral  anilin  dyes  gives  good  results. 

A  very  promising  method  recommended  by  Meyer  (95)  consists 
in  injecting  subcutaneously  about  20  c.c.  of  normal  salt  solution  contain- 
ing from  \cJo  to  4^  of  methylene-blue  into  a  young  rabbit,  and  repeating 
the  operation  in  one  to  two  hours.  Within  the  next  two  hours  the  animal 
usually  dies  and  the  central  nervous  organs  are  then  removed  and  small 
pieces  fixed  according  to  Bethe' s  method. 

The  method  of  Chr.  Sihler  may  be  recommended  for  demonstrating 
the  nerve-endings  in  striated  muscle  :  Muscle  bundles  of  the  thickness 
of  a  goose  quill  are  first  placed  for  eighteen  hours  in  a  solution  composed 
of  acetic  acid  i  vol.,  glycerin  i  vol.,  and  1%  solution  of  chloral  hydrate 
6  vols.,  and  then  teased  in  pure  glycerin.     Afterward  they  are  placed  in  a 


THE    NERVOUS    TISSUES.  1 85 

mixture  of  Ehrlich's  hematoxylin  i  vol. ,  glycerin  i  vol. ,  and  i  %  chloral  hy- 
drate solution  6  vols. ,  in  which  the  specimens  are  allowed  to  remain  for  from 
three  to  ten  days.  The  pieces  are  now  placed  in  glycerin  acidified  with 
acetic  acid  (solution  No.  i),  in  which  the  color  becomes  differentiated, 
the  nerves  and  nerve-endings  in  the  muscles  and  vessels  being  deeply 
stained,  while  the  remaining  portion  of  the  specimen  becomes  decolor- 
ized. After  having  stained  with  No.  2,  the  pieces  may  be  preserved  in 
pure  glycerin,  to  be  treated  later  with  acetic  acid  (solution  No.  i). 

These  methods  are  most  successful  in  reptilia  and  mammalia,  more 
difficult  in  the  other  classes  of  vertebrate  animals. 


SPECIAL  HISTOLOGY. 


I.  BLOOD  AND  BLOOD-FORMING  ORGANS,  HEART. 
BLOOD-VESSELS,  AND  LYMPH-VESSELS. 

A.  BLOOD  AND  LYMPH. 

J.  FORMATION  OF  BLOOD. 

Early  in  the  development  of  the  embryo  there  appear  in  a  por- 
tion of  the  extra-embryonic  area  of  the  blastoderm,  known  as  the 
area  vasculosa,  definite  masses  of  cells,  derived  from  the  mesen- 
chyme, and  spoken  of  as  blood  islands,  which  are  intimately  connected 
with  the  formation  of  the  blood.  If  these  blood  islands  be  examined 
at  a  certain  stage,  free  cells  are  seen  lying  in  their  center,  appar- 
ently derived  from  the  central  cells  of  the  islands  ;  the  cells  sur- 
rounding them  represent  the  elements  which  later  go  to  form  the 
primitive  vascular  walls.  The  free  elements  are  the  first  blood-cells 
of  the  embryo.  The  blood-cells  thus  developed  enter  the  circula- 
tion by  means  of  blood  channels  formed  by  the  confluence  of  the 
blood  islands.  These  grow  toward  the  embryo  and  later  join  the 
large  central  vessels.  The  origin  of  these  blood  islands  is  still  an 
open  question.  Some  authors  contend  that  they  arise  from  the 
mesoblast  (P.  Mayer,  87,  93  ;  K.  Ziegler ;  van  der  Stricht,  92), 
others  that  they  are  of  entodermic  origin  (Kupfifer,  78  ;  Gensch ; 
Rückert,  88  ;  C.  K.  Hoffmann,  93,  I ;  93,  II ;  Mehnert,  96).  At  a 
certain  period  the  embryonic  blood  consists  principally  of  nucleated 
red  cells,  which  proliferate  in  the  circulation  by  indirect  division. 
The  colorless  blood-cells,  the  development  of  which  is  not  yet  fully 
understood,  appear  later.  It  is  possible  that  they  also  are  elements 
of  the  blood  islands,  which  do  not  contain  any  hemoglobin.  In  a 
later  period  of  embryonic  life  the  liver  becomes  a  blood-forming 
organ.  Recent  investigations  have,  however,  shown  that  it  does 
not  take  a  direct  part  in  the  formation  of  the  blood,  but  only 
serves  as  an  area  in  which  the  blood-corpuscles  proliferate  during 
their  slow  passage  through  its  vessels.  The  blind  sac-like  endings 
of  the  venous  capillaries  seem  to  be  particularly  adapted  for  this 
purpose,  as  in  them  the  blood  current  stagnates,  and  it  is  here  that 
the  greater  number  of  blood-cells  reveal  mitotic  figures.  The 
newly  formed  elements  are  finally  swept  away  by  the  blood  stream 
and  enter  the  general  circulation  (van  der  Stricht,  92  ;  v.  Kostan- 
ecki,  92,  III).      Many  investigators  believe  that  the  red  blood-cells 

186 


BLOOD    AND    LYMPH.  1 8/ 

have  an  entirely  different  origin  in  the  Hver — namely,  from  the  large 
polynuclear,  giant  cells,  which  are  thought  to  arise  either  from  the 
cells  of  the  capillaries  or  from  the  liver-cells  (Kuborn,  M.  Schmidt). 

Late  in  fetal  life  and  in  the  adult,  the  red  bone-marrow  and  the 
spleen  are  the  organs  which  form  the  red  blood-cells.  The  lym- 
phatic glands  and  the  spleen  produce  the  white  blood-cells.  In  ad- 
dition to  the  nucleated  red  corpuscles  which  are  present  up  to  a  cer- 
tain stage  of  development,  nonnucleated  red  blood-cells  also  appear. 
The  number  of  the  latter  increases,  until  finally  they  are  found 
almost  exclusively  in  the  blood  of  the  new-born  infant. 

The  blood  of  the  adult  consists  of  a  fluid,  coagulable  substance, 
the  blood  plasma,  and  of  formed  elements  suspended  in  this  inter- 
cellular substance.  The  fluid  medium  of  the  blood  is  of  a  clear 
yellowish  color  and  of  alkaline  reaction,  having  a  specific  gravity 
of  about  1030.  It  is  made  up  of  water,  of  which  it  contains  about 
90^,  and  various  organic  and  inorganic  substances.  The  formed 
elements  are :  {a)  Red  blood-corpuscles  (erythrocytes) ;  {b)  white 
blood-corpuscles  (leucocytes) ;  and  {c)  the  blood  platelets  of  Biz- 
zozero  (82),  hematoblasts  of  Hayem,  or  the  thrombocytes  of 
Dekhuysen.  Besides  these,  there  are  present  particles  of  fat,  and, 
as  H.  F.  Müller  (96)  has  recently  shown,  also  hemokonia. 

2.  RED  BLOOD-CORPUSCLES. 

In  man  and  nearly  all  mammalia  the  great  majority  of  the  red 
blood-corpuscles  are  nonnucleated,  biconcave  circular  discs  with 
rounded  edges.  They  have  smooth  surfaces,  are  transparent,  pale 
yellowish-red  in  color,  and  very  elastic.  No  method  has  as  yet 
been  devised  to  demonstrate  a  nucleus  in  these  cells,  and  there  is  no 
doubt  that  the  red  blood-discs  of  the  human  adult  and  of  mammalia 
are  devoid,  in  the  histologic  sense,  of  a  nucleus  capable  of  differen- 
tiation (compare  Lavdowsky ;  Arnold,  96).  They  are  therefore 
peculiarly  modified  cells.  They  possess  a  somewhat  more  resistant 
external  zone  of  exoplasm,  which  has  been  interpreted  as  a  cell 
membrane  by  certain  observers  (Lavdowsky),  but  which  does 
not  present  the  characteristics  of  a  true  cell  membrane. 

If  fresh  blood  be  left  for  some  time  undisturbed,  the  blood-discs 
adhere  to  each  other  by  their  flattened  surfaces,  grouping  them- 
selves in  rotileaux. 

By  certain  reagents  the  clear  and  transparent  contents  of  the 
blood-corpuscles  can  be  separated  into  two  substances — a  staining 
and  a  nonstaining.  The  first  consists  of  the  blood  pigment,  or 
hemoglobin,  which  can  be  dissolved  ;  the  second  of  a  colorless  sub- 
stance, the  stroma,  which  presents  itself  in  various  forms  (protoplasm 
of  the  cell).  The  stroma  probably  contains  the  hemoglobin  in  solution. 

Hemoglobin  is  a  very  complex  proteid  which  may  be  decom- 
posed into  a  globulin  and  a  pigment  hematin.  The  hemoglobin  of 
the  majority  of  animals  crystallizes  in  the  form  of  rhombic  prisms  ; 


1 88  BLOOD    AND    BLOOD-FORMING    ORGANS. 

in  the  squirrel,  however,  in  hexagonal  plates,  and  in  the  guinea-pig 
in  tetrahedra.  Hematin  combines  with  hydrochloric  acid  to  form 
heinin,  or  Teichniann' s  crystals,  of  brownish  color,  rhombic  shape, 
and  microscopic  size.  They  are  of  much  value  in  lego-medical 
work,  since  they  may  be  obtained  from  blood,  no  matter  how  old, 
and  are  characteristic  of  hemoglobin.  They  may  be  obtained 
from  very  small  quantities  of  blood  pigment. 

If  a  small  drop  of  blood  pressed  from  a  small  puncture  is 
placed  on  a  slide  and  covered  with  a  cover-glass,  the  red  blood- 
cells  soon  become  changed.  This  is  due  to  the  evaporation  of 
water  in  the  blood  plasma,  causing  an  increased  concentration  of 
the  sodium  chloride  contained,  which  in  turn  draws  water  from  the 
blood-cells     The  shrinkage  which  follows  produces  a  characteristic 


Fig.  151. — Hu- 
man red  blood-cells  ; 
X  1500  :  a,  As  seen 
from  the  surface  ;  b, 
as  seen  from  the  ed^e. 


Fig.  152. — So-called 
"rouleau"  formation  of 
human  erythrocytes ;  X 
1500. 


Fig.  153. — Hemin,  or 
Teichmann' s  crystals,  from 
blood  stains  on  a  cloth. 


Fig.  154. — "  Crenated"  human  red  blood- 
cells;  X  1500- 


F'g-  '55- — Red  blood-corpuscles  sub- 
jected to  the  action  of  water  ;  X  15^^°  •  '^i 
Spheric  blood-cell;   b,  "blood  shadow." 


change  in  the  form  of  the  cells,  which  assume  a  crenated  or  stellate 
shape.  The  red  blood-cells  of  blood  mounted  in  normal  salt 
become  crenated  in  a  short  time  for  the  same  reason.  Red  blood- 
cells  are  variously  affected  by  different  fluids.  In  water  they  become 
spheric  and  lose  their  hemoglobin  by  solution.  Their  remains  then 
appear  as  clear,  spheric,  indistinct  blood  shadows,  which  may,  how- 
ever, be  again  rendered  distinct  by  staining  with  iodin.  Dilute 
acetic  acid  has  a  similar  but  more  rapid  action,  with  this  peculiarity, 
that  before  becoming  paler  the  blood-cells  momentarily  assume  a 
darker  hue.  Bile,  even  when  taken  from  the  animal  furnishing  the 
blood,  exerts  a  peculiar  influence  upon  the  red  blood-cells  ;  they 
first  become  distended,  and  then  suddenly  appear  to  explode  into 


BLOOD    AND    LYMPH, 


189 


small  fragments.  Dilute  solutions  of  tannic  acid  cause  the  hemo- 
globin to  leave  the  blood-cells,  and  coagulate  in  the  form  of  a  small 
globule  at  the  edge  of  the  blood-cell.  In  alkalies  of  moderate 
strength  the  red  blood-cells  break  down  in  a  few  moments. 

Besides  the  disc-shaped  red  blood-cells,  every  well-made  prep- 
aration shows  a  few  small,  spheric,  nonnucleated  cells  containing 
hemoglobin.  These,  however,  have  received  as  yet  but  little 
attention. 

M.  Bathe  makes  the  statement  that  human  blood  and  the  blood  of 
mammalia  contain  corpuscles  of  different  sizes,  bearing  a  definite  numerical 
relationship  to  each  other,  '*  If  they  be  classified  according  to  their  size, 
and  the  percentage  of  each  class  be  calculated,  the  result  will  show  a 
nearly  constant  proportional  graphic  curve  varying  but  slightly,  according 


Fig.  156. — Red  blood-corpuscles  from  various  vertebrate  animals  ;  X  looo  (Welker's 
model)  :  a,  From  proteus  (01m)  ;  b,  from  frog  ;  c,  from  lizard  ;  d,  from  sparrow  ;  e,  from 
camel  ;  f&nAg,  from  man  ;  k,  from  myoxus  glis  ;  i,  from  goat ;  k,  from  musk-deer. 


to  the  animal  species."  According  to  M.  Bethe,  dry  preparations  of 
human  and  animal  blood  may  be  distinguished  from  each  other,  with  the 
exception  of  the  blood  of  the  guinea-pig  which  presents  a  curve  identical 
with  that  of  human  blood. 

The  red  blood-cells  of  mammalia,  excepting  those  of  the  llama 
and  camel  species,  are  in  shape  and  structure  similar  to  those  of 
man.  The  red  blood-cells  of  the  llama  and  camel  have  the  shape 
of  an  ellipsoid,  flattened  at  its  short  axis,  but  also  nonnucleated. 

We  have  already  made  mention  of  the  fact  that  the  embryonal 
erythrocytes  are  nucleated  ;  the  question  now  arises  as  to  how,  in 
the  course  of  their  development,  they  lose  their  nuclei.  Three  pos- 
sibilities confront  us  :  First,  either  the  embryonal  blood-cells  are 
destroyed  and  gradually  replaced  by  previously  existing  nonnucle- 


190 


BLOOD    AND    BLOOD-FORMING    ORGANS. 


ated  elements  ;  or,  second,  the  nonnucleated  red  cells  are  formed 
from  the  nucleated  by  an  absorption  of  the  nucleus  (or  what  appears 
to  be  such  to  the  eye  of  the  observer,  Arnold,  96)  ;  or,  finally,  the 
nucleus  is  extruded  from  the  original  nucleated  cell.  According  to 
recent  investigations  (Howell)  the  third  possibility  represents  the 
change  as  it  actually  takes  place. 

In  all  vertebrate  animals  except  mammalia,  the  red  blood- 
corpuscles  are  nucleated.  They  are  elliptic  discs  with  a  biconvex 
center  corresponding  to  the  position  of  the  nucleus.  The  blood- 
cells  of  the  amphibia  (frog)  are  well  adapted  for  study  on  account 
of  their  size.  They  are  long  and,  as  a  rule,  contain  an  elongated 
nucleus  with  a  coarse,  dense  chromatin  framework,  which  gives 
them  an  almost  homogeneous  appearance.  The  cell-body  may  be 
divided,  as  in  mammalia,  into  stroma  and  hemoglobin.  When  sub- 
jected to  certain  reagents,  the  contour  of  the  cells  appears  double 
and  sharply  defined.  This  condition  is,  however,  no  proof  of  the 
existence  of  a  membrane.  The  blood-cells  of  birds,  reptiles  and 
fishes  are  similarly  constructed. 

The  diameter  of  the  erythrocytes  varies  greatly  in  different  ver- 
tebrate animals,  but  is  constant  in  each  species.  The  red  blood-cells 
of  man  measure  on  the  average  7.5  //  (7.2  /^  to  7.8  fx),  in  their  long 
diameter,  and  1.6  p.  to  1.9//  in  their  short  diameter.  We  append 
a  table  of  their  number  in  a  cubic  millimeter  and  size  in  man  and 
certain  animals  as  compiled  by  Rollett  (71,  II)  and  M.  Bethe  : 


Species. 

Man       {Homo)    .... 

Monkey .  [Cercopitk.  ruber) 

Hare {Lepus  cutticulus) 

Guinea-pig {Cavia  cob.)    .    . 

Dog [Canis fam.)  .    . 

Cat {Felis  do77i.)    .    . 

Horse {Equuscab.)  .    . 

Musk-deer {Moschus  jav.)   . 

Spanish  goat {Capra  his.) 

Domestic  chaffinch  ....  {Fringilla  dorn. ) 

Dove {Columba)  .    .    . 

Chicken ( Callus  dorn. )     . 

Duck {Anas  bosch.) 

Tortoise {Testudo  grceca) 

Lizard {Lacerta  agil.) 

Snake {Coluber  natr.) 

Frog .  {Rana  temp.) 

Toad {Bufo  vulg.)  . 

Triton {Triton  crist.) 


Size. 

7.2-7.8// 

7.16 


7-4« 

7.2 

6.2 


5.58 

2.5 

4.25    . 

Length, 

Breadth, 

L. 

B. 

L. 

B. 

L. 

B. 

L. 

B. 

L. 

B. 

L. 

B. 

L. 

B. 

L. 

B. 

L. 

B. 


No.  IN 
Cubic  Milli- 
meter. 

5,000,000 
6,355.000 
6,410,000 
5,859,500 
6,650,000 
9,900,000 
7,403,500 


II. 9 

6.8 

14.7 

6.5 
12. 1 

7.2 
12.9 

8.0 
21.2 
12.45 
15-75 

9.1 
22.0 
13.0 
22.3 

15-7 
21.8 

15-9 
29-3 
19-5 


19,000,000 


2,010  000 


629,000 
1,292,000 
829,400 
393,200 
389,000 
103,000 


BLOOD    AND    LYMPH. 


191 


Species.  Size. 

Salamander {Salamattdra  mac.)  .    .  Length,  37.8 

Breadth,  23.8 

(Proteus  align.)      .    .    .  L.  5^ 

B.  35 

Sturgeon iAcipenser  Si.)    .    .    .    .  L.  13.4 

^  B.  10.4 

Carp [Cyprinus  Gobio)    .    .    .  L.  17.7 

B.  10. 1 


No.  IN 

Cubic  Milli- 
meter. 

.    .       80,000 


35,000 


3.  WHITE  BLOOD-CORPUSCLES. 

The  white  blood-cells  contain  no  hemoglobin  and  are  nucleated 
elements  which,  under  certain  conditions,  possess  ameboid  move- 
ment. Their  size  varies  from  5  /^  to  12  //,  and  they  are  less  numer- 
ous than  the  red  blood-corpuscles,  one  white  blood-cell  to  from 
three  hundred  to  five  hundred  red  cells  being  a  normal  proportion. 


Fig.  157.— From  the  normal  blood  of  man;  X  1200  (from  dry  preparation  of  H. 
F.  Müller)  :  a,  Red  blood-cell ;  b,  lymphocyte  ;  c  and  d,  mononuclear  leucocytes ;  e, 
transitional  leucocyte  ;  /  and  g,  leucocytes  with  polymorphous  nuclei. 

Flemming  ascribes  a  fibrillar  structure  to  the  protoplasm  of  white 
blood-cells,  and  was  the  first  to  observe  a  centrosome  situated  near 
the  nucleus.  M.  Heidenhain  made  the  observation  that  the  white 
blood-cells  possessed  several  centrosomes  grouped  to  constitute  a 
microcenter  (microcentrum)  about  which  the  fibrillar  structure  of  the 
protoplasm  was  arranged  radially.  The  meshes  of  the  fibrillar  net- 
work are  filled  with  a  more  fluid  interfibrillar  substance,  in  which  are 
found  the  specific  granules  to  be  mentioned  later.  In  the  normal 
blood  the  white  blood-cells  vary  in  size  and  structure,  and  the  fol- 
lowing varieties  are  distinguished  :  (i)  Small  and  large  lymphocytes  ; 
(2)  mononuclear  leucocytes  ;  (3)  transitional  leucocytes  ;  (4)  leuco- 
cytes, either  polymorphonuclear  or  polynuclear. 

The    lymphocytes    form    about    20^    of  the   white   blood-cells. 


192 


BLOOD    AND    BLOOD-FORMING    ORGANS. 


They  vary  in  size  from  5  /^  to  7. 5  //  and  possess  a  relatively  large 
nucleus,  the  chromatin  of  which  is  in  the  form  of  relatively  large 
granules,  which  stain  rather  deeply.  The  nucleus  is  surrounded  by 
a  narrow  zone  of  protoplasm,  often  seen  clearly  only  to  one  side  of 
the  cell  in  the  form  of  a  crescent.  It  does  not  stain  readily  in  acid 
dyes. 

The  leucocytes  vary  in  size  from  y  ji  to  10  //.  The  mononuclear 
leucocytes,  constituting  about  2^  to  4^  of  the  white  blood-cells, 
have  a  nearly  round  or  oval  nucleus,  which  usually  does  not  stain 
very  deeply,  and  which  is  relatively  smaller  than  that  of  the  lympho- 
cytes. The  transitional  leucocytes,  forming  also  about  2^  to 
4^  of  the  white  blood-cells,  are  developed  from  the  mononuclear 
variety  and  represent  transitional  stages  in  the  development  of 
mononuclear  leucocytes  to  those  with  polymorphous  nuclei.  The 
nucleus  in  the  transitional  form  is  similar  in  size  and  structure  to  that 
of  the  mononuclear  variety,  but  of  a  more  or  less  pronounced  horse- 
shoe-shape. The  leucocytes  with  polymorphous  nuclei,  developed 
from  the  transitional  forms,  are  very  numerous  in  the  blood,  form- 
ing about  70^  of  the  entire  number  of  white  blood-cells.  They 
are  also  the  cells  which  show  the  most  active  ameboid  movement 
when  examined  on  the  warm  stage.  They  possess  variously  lobu- 
lated  nuclei,  the  several  nuclear  masses  often  being  united  by  del- 
icate threads  of  nuclear  substance.  A  leucocyte  with  a  poly- 
morphous nucleus  becomes  a  polynuclear  cell  in  case  the  bridges 
of  nuclear  substance  uniting  the  several  lobules  of  the  nucleus  break 
through.  In  the  protoplasm  of  the  transitional  leucocytes,  the 
polymorphonuclear,  and  the  polynuclear  forms  are  found  fine  and 
coarse  granules.     Our  knowledge  of  these  granules  has,  however. 


at  ß  y  Ö 

Fig.  158. — Ehrlich' s  leucocytic  granules;  X  1800  (from  preparations  of  H.  P". 
Müller)  :  a,  Acidophile  or  eosinophile  granules,  relatively  large  and  regularly  distributed  ; 
£,  neutrophile  granules ;  ß,  amphophile  granules,  few  in  number  and  irregularly  dis- 
tributed ;  y,  mast  cells  with  granules  of  various  sizes  ;  6,  basophile  granules,  (a,  6,  and 
e,  From  the  normal  blood ;  7,  from  human  leukemic  blood ;  ß,  from  the  blood  of 
guinea-pig.) 


been  greatly  extended  since  Ehrlich  has  shown  that  the  granules  of 
leucocytes  show  specific  reactions  toward  certain  anilin  stains,  or 
combinations  of  such  stains.  He  divides  the  granules  of  the  leuco- 
cytes into  five  classes  which  he  terms  respectively  a-,  /5-,  3-,  y-,  and  e- 
granules.  In  human  blood  are  found  the  «-granules,  which  show  an 
affinity  for  acid-anilin  stains,  are  therefore  known  as  acidophile  gran- 


BLOOD    AND    LYMPH.  1 93 

ules,  and,  since  they  are  most  readily  stained  in  eosin,  are  generally 
spoken  of  as  eosinophile  granules.  In  normal  blood  from  i  ^  to  4^ 
of  the  polymorphonuclear  leucocytes  and  now  and  then  a  transi- 
tional cell  have  eosinophile  granules.  The  granules  are  coarse  and 
stain  bright  red  in  eosin.  Nearly  all  the  leucocytes  with  granules 
(from  65  ^0  to  68  ^  of  all  white  blood-cells)  have  ^-granules  or, 
since  they  are  stained  in  color  mixtures  formed  by  a  combination  of 
acid  and  basic  anilin  stains,  neutrophile  granules.  The  neutrophile 
granules  are  much  finer  than  the  eosinophile  and  are  not  stained 
in  acid  stains.  The  y-  and  ^-granules  are  stained  in  basic  anilin 
stains,  and  are  known  as  basophile  granules.  They  are  coarse  and 
irregular,  and  the  leucocytes  containing  them  form  from  o.  5  %  to 
I  ^  of  the  white  blood-cells. 

It  cannot  at  this  time  be  definitely  stated  whether  the  different 
varieties  of  granules  are  to  be  looked  upon  as  specific  products  of 
the  protoplasm  of  the  leucocytes,  possibly  of  the  nature  of  granules 
which  may  be  likened  to  the  secretory  granules  of  glandular  cells, 
or  whether  they  are  to  be  regarded  as  cell  inclusions.  It  has  also 
not  been  clearly  shown  whether  one  variety  of  granules  may  develop 
into  another  variety, — neutrophile  into  eosinophile, — although  this 
has  been  suggested.  According  to  Weidenreich,  eosinophile  gran- 
ules are  thought  to  represent  fragments  of  erythrocytes,  enclosed 
within  the  protoplasm  of  leucocytes. 

The  polymorphism  of  the  leucocyte-nucleus  has  induced  many 
investigators  to  advance  the  theory  that  a  direct  division  takes  place 
(fragmentation — Arnold,  Löwit).  Flemming  (91,  III),  however, 
succeeded  in  demonstrating  that  true  mitotic  processes  actually  take 
place,  so  that  in  this  respect  there  really  exists  no  difference  between 
leucocytes  and  other  cells  (compare  also  H.  F.  Müller,  89,  91).  It 
is  only  in  the  formation  of  polynuclear  leucocytes  that  the  poly- 
morphous nucleus  sometimes  undergoes  a  fragmentation  process 
which  results  in  several  parts.  But  even  in  this  case  pluripolar 
mitoses  have  been  observed.  A  division  of  the  cell-body  subse- 
quent to  that  of  the  nucleus  is  lacking  in  the  processes  just 
described.  As  a  result  a  single  cell  with  several  nuclei  is  formed 
(polykaryocyte).     The  fate  of  such  cells  is  still  in  doubt. 

The  extraordinary  motility  which  most  leucocytes  possess,  is  in 
great  part  responsible  for  their  wide  distribution,  even  outside  of 
the  vascular  system.  They  have  the  power  of  creeping  through 
the  walls  of  the  capillaries  (diapedesis,  Cohnheim  67,  I),  and  of 
penetrating  into  the  smallest  connective-tissue  clefts,  between  the 
cells  of  epithelia,  etc.,  whence  they  either  pass  on  (migratory  cells) 
or  remain  stationary  for  a  time.  An  important  function  falls  to  the 
lot  of  the  leucocytes  in  the  absorption  of  superfluous  tissue  particles 
or  in  the  removal  of  foreign  bodies  from  certain  regions  of  the  body. 
In  the  first  case  they  take  part  in  a  process  of  tissue-disintegration  ; 
in  the  second,  they  take  up  the  particles  by  means  of  their  pseudo- 
podia  for  the  purpose  either  of  assimilation  or  of  removal  (phago- 
^3 


194  BLOOD    AND    BLOOD-FORMING    ORGANS. 

cytes).  It  may  be  readily  understood  that  the  latter  function  of  the 
leucocytes  is  of  the  greatest  importance  in  certain  pathologic  pro- 
cesses. 

It  is  somewhat  venturesome  at  the  present  state  of  our  knowl- 
edge to  make  definite  statements  as  to  the  origin  in  postembryonic 
life  of  the  various  forms  of  white  blood-cells  above  described.  The 
following  statement,  however,  seems  warranted  from  the  evidence 
at  hand. 

The  lymphocytes  would  seem  to  be  developed  in  the  meshes  of 
adenoid  tissue,  especially  in  the  so-called  ^^/v/z  centers  of  Flemming, 
m  the  adenoid  tissue  of  lymph-glands  and  lymph-follicles  (see  under 
these).  Here  the  cells  undergo  active  karyokinetic  division,  but 
where  the  cells  which  pass  through  the  process  originate  is  a  matter 
concerning  which  there  is  a  difference  of  opinion.  Some  investi- 
gators believe  that  they  penetrate  the  germ  centers  with  the  lymph, 
and  find  there  a  suitable  place  for  division.  Again,  others  see  in 
Flemming's  germ  centers  permanent  organs  whose  elements  remain 
stationary  and  supply  the  blood  with  a  continuous  quota  of  lympho- 
cytes. Be  this  as  it  may,  the  fact  remains  that  the  germ  centers 
are  the  most  important  regions  for  the  formation  of  lymphocytes. 
From  these  they  pass  out  with  the  lymph  current  into  the  blood 
circulation,  or  directly  into  the  blood-vessels,  there  to  enter  upon  the 
functions  which  they  are  called  upon  to  perform.  The  leucocytes 
with  neutrophile  granules  are  probably  developed  in  the  blood  and 
lymph  from  mononuclear  leucocytes  which  have  their  origin  in  the 
spleen  pulp,  possibly  also  in  the  bone-marrow.  The  leucocytes  of 
circulating  blood  with  eosinophile  granules  in  all  probability  come 
from  mononuclear  cells  with  such  granules  found  in  bone-marrow. 
Under  certain  conditions  it  would  seem  that  they  also  develop  in 
connective  tissue.  The  leucocytes  with  the  basophile  granules  prob- 
ably enter  the  circulation  from  the  connective  tissue  of  certain  re- 
gions. The  lymphocytes  and  leucocytes  found  in  the  blood  are  also 
found  in  the  lymph-vessels  and  lymph-spaces. 

4.   BLOOD  PLATELETS— THROMBOCYTES, 

The  third  element  of  the  blood  is  the  d/ood  platelets  (Bizzozero) 
{blood-placgues,  Laker ;  hematoblasts,  Hayem  ;  thrombocytes,  Deck- 
huysen).  They  are  extremely  delicate  and  transitory  structures,  whose 
existence  in  the  living  blood  was  denied  for  a  long  time  by  many  in- 
vestigators, but  whose  presence  in  the  wing  vessels  of  the  living  bat 
was  conclusively  demonstrated  by  Laker  (84).  They  are  free  from 
hemoglobin,  are  of  round  or  oval  shape,  and  in  mammals  measure 
about  3  //  in  diameter.  Owing  to  the  fact  that  they  readily  clump 
together  when  blood  leaves  the  vessels,  and  undergo  change,  it  is 
somewhat  difficult  to  give  an  estimate  of  their  number.  They  are 
said  to  be  present  in  human  blood  to  the  extent  of  200,000  to 
300,000  in  every  cubic  millimeter.      By  the  exercise  of  great  care 


BLOOD    AND    LYMPH, 


19s 


and  the  employment  of  special  methods  on  the  part  of  a  number 
of  recent  observers  (Detjen,  Deckhuysen,  Kopsch  and  Argutinsky), 
they  have  been  able  to  show  that  these  structures  present  a  more 
compHcated  structure  than  was  formerly  thought.  When  exam- 
ined in  an  isotonic  salt  solution  (for  mammals  0.9  to  0.95  sodium 
chlorid  solution),  they  present  an  oval  or  short  spindle-shaped  form, 
and  in  them  there  can  be  made  out  a  relatively  large  structure,  which 
stains  in  certain  basic  aniline  stains  and  is  interpreted  as  a  nucleus 
(Deckhuysen).  When  examined  after 
a  method  suggested  by  Detjen  (with  a 
I  per  cent,  agar  solution  there  is 
mixed  0.6  per  cent,  sodium  chlorid, 
0.3  per  cent,  of  sodium  metaphos- 
phate  and  dipotassium  phosphate;  a 
thin  layer  of  this  agar  mixture  is 
spread  on  the  slide  and  a  drop  of 
blood  mounted  between  it  and  the 
cover),  the  blood  platelets  or  throm- 
bocytes may  be  observed  on  the  warm 
stage  for  several  hours,  and  it  may  be 
seen  that  they  present  ameboid  move- 
ment, in  that  short,  thread-like  pro- 
cesses pass  out  from  the  cell,  which 
may  alter  their  shape  and  position 
and  which  may  be  again  withdrawn. 

When  the  blood  leaves  the  blood- 
vessels, the  blood  platelets  or  throm- 
bocytes break  down  very  quickly, 
unless  the  above-mentioned  methods 
are  made   use  of,  so  that  in  ordinary 

fresh  preparations  or  generally  in  dried  films  they  are  not  to  be 
observed  in  an  unaltered  state.  The  nuclei  disappear  and  the  pro- 
toplasm becomes  granular  or  vacuolated.  The  breaking  down  of 
the  blood  platelets  or  thrombocytes  is  accompanied  by  the  forma- 
tion of  fibrin  (coagulation  of  the  blood),  the  fibrin  threads  beginning 
at  the  borders  or  processes  of  the  platelets,  and  radiating  in  all 
directions  (Kopsch). 

Hemokonia. — H.  F.  Müller  (96)  found  in  the  blood  of  healthy  and 
diseased  individuals  highly  refractive,  colorless,  and  round  (seldom  rod- 
like) bodies,  which  he  terms  "hemokonia."  Their  numbers  vary, 
although  they  are  normal  constituents  of  the  blood.  Their  nature  and 
origin  are  obscure.  They  do  not  dissolve  in  acetic  acid,  nor  are  they 
blackened  by  osmic  acid.  The  latter  would  seem  to  indicate  that  they 
do  not  consist  of  ordinary  fat  substance,  although  they  are  probably  com- 
posed of  a  substance  closely  allied  to  fat.  They  are  usually  i  /i  in  diam- 
eter. 


Fig.    159. — Fibrin    from   laryngeal 
vessel  of  child  ;  X  about  300. 


IQÖ  BLOOD    AND    BLOOD-FORMING    ORGANS. 

5.  BEHAVIOR  OF  BLOOD-CELLS  IN  THE  BLOOD  CURRENT. 

In  the  circulating  blood  the  behavior  of  the  formed  elements 
varies.  The  more  rapid  axial  current  contains  very  nearly  all  the 
erythrocytes,  and  as  a  consequence  very  few  are  found  adjacent  to  the 
walls  of  the  vessels.  In  the  peripheral  current,  on  the  other  hand, 
are  found  most  of  the  leucocytes,  and  in  a  retarded  circulation  they 
are  seen  to  glide  along  the  walls  of  the  vessels.  At  the  bifurcations 
of  the  vessels,  especially  of  the  capillaries,  the  erythrocytes  are 
sometimes  caught  and  elongated  by  the  division  of  the  current,  the 
one-half  of  the  cell  extending  into  the  one  and  the  other  half  into 
the  other  branch  of  the  vessel,  while  the  corpuscle  oscillates  back 
and  forth.  When  again  free  the  cell  immediately  resumes  its  original 
shape.  From  this  it  is  seen  that  erythrocytes  are  very  elastic 
structures.  In  the  smaller  vessels  and  capillaries,  especially  when 
the  latter  are  altered  by  pathologic  conditions,  the  leucocytes  may 
be  seen  passing  out  of  the  vessels,  and  it  would  seem  that  they  are 
able  to  penetrate  through  the  walls  and  even  through  the  endo- 
thelial cells  lining  the  blood-vessels  (compare  also  Kolossow,  93). 
First,  they  send  out  a  fine  process,  which  is  probably  endowed  with 
a  solvent  action.  This  penetrates  the  wall  of  the  vessel,  after  which 
the  remainder  of  the  cell  pushes  its  way  through  slowly. 


B.  LYMPHOID  TISSUE,  LYMPH-NODULES,  AND  LYMPH- 
GLANDS. 

As  to  the  origin  of  lymphoid  tissue,  the  lymph-glands,  and  the 
spleen,  there  is  still  considerable  difference  of  opinion.  Most 
authors  believe  that  these  structures  are  developed  from  the  middle 
germinal  layer  (Stohr,  89;  Paneth  ;  J.  Schaffer,  91  ;  Tomarkin). 
Others  believe  in  an  entodermic  origin  (Kupffer,  92  ;  Retterer  ; 
Klaatsch  ;   C.  K.  Hoffmann,  93,  II). 

The  framework  of  lymphoid  tissue  is  a  reticular  connective  tis- 
sue (adenoid  connective  tissue — His,  61),  This  consists  of  a  net- 
work of  fine  fibrils  of  reticular  and  white  fibrous  connective  tissue 
and  of  cells  (endoplasm  and  nuclei)  which  are  situated  on  the 
reticulum,  often  at  nodal  points.  Within  its  meshes  the  lymph-cells 
lie  in  such  numbers  and  so  densely  arranged  that  on  microscopic 
examination  the  network  is  almost  entirely  covered  unless  very  thin 
sections  are  used.  The  cells  may  be  removed  from  the  meshes  of 
the  reticulum  by  stippling  and  brushing  section  with  a  fine  brush  or 
by  placing  sections  in  a  test-tube  partly  filled  with  water  and  sub- 
jecting them  to  vigorous  shaking,  or,  still  better,  by  subjecting 
sections  or  pieces  of  lymphoid   tissue  to  digestion  with  pancreatin. 

Lymph  tissue  may  be  diffuse,  as  in  the  mucous  membrane  of  the 
air-passages  and  as  in  that  of  the  intestinal  tract,  uterus,  etc.  (znd. 
Sauer,  96).     Lymphoid  tissue  may  be  also  sharply  defined  in  the 


LYMPHOID    TISSUE,    LYMPH-NODULES,    AND    LYMPH-GLANDS.      1 9/ 

form  of  round  nodules,  simple  follicles  or  nodules.  These  are  either 
single,  solitary  lymph-follicles,  or  gathered  into  groups,  agminated 
lymph -nodules.  They  are  found  scattered  in  the  mucous  mem- 
brane of  the  mouth,  pharynx,  and  intestine.  In  lymph-nodules  also 
we  find  the  characteristic  lymph-cells  and  the  adenoid  reticulum. 
As  a  rule,  the  former  are  arranged  concentrically  at  the  periphery ; 
and  in  the  center  of  the  nodule  the  reticular  tissue  usually  has  wider 
meshes,  and  the  lymph-cells  are  less  densely  placed.  (Fig.  1 60.) 
In  the  center  of  the  nodule  the  cells  often  show  numerous  mitoses, 
and  it  is  here  that  an  active  proliferation  of  the  cells  takes  place. 
The  cells  may  either  remain  in  the  lymph-follicle  or  the  newly 
formed  cells  are  pushed  to  the  periphery  of  the  nodule,  and  are  then 
swept  into  the  circulation  by  the  slow  lymph  current  which  circu- 
lates between  the  wide  meshes  of  the  reticular  connective  tissue. 
Flemming  (85,  II)  has  called  that  central  part  of  the  nodule  con- 
taining the  proliferating  cells  the  germ  center  or  secondary  nodule 
(compare  p.  194).  The  germ  centers  are  transitory  structures,  and 
are  consequently  found  in  different  stages  of  development.  They 
may  even  be  absent  for  a  time. 


Gland. j3s|^4«9^^"ö''«''''äSf fess 


,^'^e.Sa«« 


Submu- 

cosa. 


Fig.  160.— A  solitary  lymph -nodule  from  the  human  colon.    At  a  is  seen  the  pronounced 
concentric  arrangement  of  the  lymph-cells. 

The  lymph-glands  are  organs  of  a  more  complicated  structure, 
but  also  consist  of  lymphoid  tissue.  They  are  situated  here  and  there 
in  the  course  of  the  lymph-vessel  and  are  widely  distributed.  Their 
size  varies  greatly.  In  shape  they  are  much  like  a  bean  or  kidney, 
and  the  indentation  on  one  side  is  known  as  the  hilutn.  The  affer- 
ent lymph-vessels,  the  vasa  afferentia,  enter  at  the  convex  surface 
of  the  organ,  while  the  efferent  vessels,  the  vasa  effcrcntia,  pass  out 


198  BLOOD    AND    BLOOD-FORMING    ORGANS. 

at  the  hilum.  The  whole  gland  is  surrounded  by  a  capsule  consist- 
ing of  two  layers :  the  outer  is  made  up  of  a  loose,  and  the  inner  of 
a  more  compact,  connective  tissue  in  which  elastic  fibers  and  a  few 
smooth  muscle-fibers  are  imbedded.  Portions  of  the  inner  layer 
pass  into  the  substance  of  the  gland  to  form  septa,  or  trabeculce,  by 
means  of  which  the  organ  is  divided  into  a  number  of  imperfectly 
separated  compartments.  These  trabeculae  may  be  very  well 
developed,  äs  in  the  lymph-glands  of  the  domestic  cattle,  or  only 


.■4§ 


Fig.  161. — Transverse  section  of  human  cervical  lymph-gland,  showing  the  general 
structure  of  a  lymph-gland  ;  X  l^.  l>g,  Blood-vessels  ;  c/,  fibrous  capsule  ;  A,  hilum  ; 
iz,  germ-center  ;  n/,  lymph-nodule  ;  sc,  cortical  substance  ;  gm,  medullary  substance  ; 
ir,  trabeculae;  v/a,  afferent  lymph-vessels;  v/e,  efferent  lymph-vessels  ("Atlas  and 
Epitome  of  Human  Histology,"  Sobotta). 

poorly  developed,  as  in  the  human  lymph-glands,  where  they  are 
often  almost  wanting.  The  lymphoid  tissue  of  the  gland  is  so 
distributed  that  at  its  periphery  a  large  number  of  more  or  less 
clearly  defined  lymph-nodules  are  found,  which  are  in  part  separated 
from  each  other  by  the  trabeculae  just  described,  the  cortical  nodules. 
The  nodules  are  structural  units  and  have  a  typical  blood  supply, 
and   are  in   structure   like   the  lymph-nodules   of  simple  and  ag- 


LYMPHOID    TISSUE,    LYMPH-NODULES,    AND    LYMPH-GLANDS.      1 99 

minated  follicles  above  mentioned.  They  form  a  peripheral  layer 
which  is,  however,  not  clearly  defined  in  the  neighborhood  of  the 
hilum.  This  layer  is  known  as  the  cortex  of  the  lymph-gland. 
(Fig.  161.)  The  lymphoid  tissue  of  the  interior  of  the  gland,  the 
medullary  substance,  is  in  the  shape  of  coxAs— medullary  cords— 
which  are  continuous  with  the  lymphoid  nodules  of  the  cortical 
portion.  These  connect  with  each  other  and  form  a  network  of 
lymphoid  tissue,  in  the  open  spaces  of  which  lie  the  trabeculae.  At 
their  periphery  the  nodules  and  medullary  cords  are  bordered  by  a 
wide-meshed  lymphatic  tissue,  the  lymph-sinus  of  the  gland,  parts 
of  which  lie  (i)  between  the  capsule  and  the  cortical  substance,  (2) 


««öl®  ß  ©  CT>f  Ob®  ®   » 


a^ii*Ä5^9^*^«« 


m 


"^^^^^^^^1^ 


Mitosis. 


Germ  center. 


Lymph-sinus. 


Medullary 
cord. 


Fie.   162.— From  a  human  lymph-gland;    X   240.      At   a    are    seen  the 
arranged  cells  of  the  lymph-nodules.      (Fixation  with  Flemmmg  s 


concentrically 
fluid.) 


between  the  nodules  of  the  latter  and  the  trabeculae,  (3)  between 
the  medullary  cords  and  the  trabecule,  and  (4)  between  the  medul- 
lary substance  and  the  capsule  at  the  hilum.  At  the  hilum  the 
loose  lymphoid  tissue  represents  a  terminal  sinus  (Toldt).  These 
sinuses  are  lined  throughout  by  endothelial  cells,  which  are  continu- 
ous with  those  of  the  afferent  and  efferent  lymph-vessels.  The 
lymph  flows  into  the  gland  through  the  afferent  vessels,  and  passes 
along  into  the  interior  through  the  spaces  offering  the  least  resist- 
ance (sinuses).  The  latter  represent  those  peripheral  portions  of 
the  nodules  and  of  the  medullary  cords  in  which  the  lymphoid  tissue 
is  present  in  loose  arrangement.    The  lymph  consequently  envelops 


200  THE    BLOOD    AND    BLOOD-FORMING    ORGANS. 

not  only  the  lymph-nodules  of  the  cortical  substance,  but  also  the 
medullary  cords,  and  finally  streams  into  the  terminal  sinus  and 
then  into  the  efferent  channels.  As  a  result  the  lymph  takes  with 
it  the  newly  formed  cells  of  the  lymph-nodules  and  the  medullary 
cords,  and  passes  out  richer  in  cellular  elements  than  on  its  entrance. 

The  lymph-glands  receive  their  blood  supply  mainly  through 
the  hilum  ;  relatively  small  arterial  branches  may  penetrate  the 
capsule.  Generally,  a  number  of  arterial  branches  enter  at  the 
hilum,  from  whence  they  may  pass  directly  into  the  medullary 
substance,  or  pass  for  a  distance  in  trabeculae.  In  their  course 
branches  are  given  off  which  pass  to  the  medullary  cords,  in  which 
they  break  up  into  capillary  vessels  situated  in  the  periphery  of  the 
cords.  These  unite  to  form  small  veins  which  anastomose  freely, 
and  unite  to  form  larger  veins.  The  cortical  nodules  receive  their 
blood  supply  from  arterial  branches  which  enter  their  proximal 
sides  (side  toward  the  hilum)  and  course  through  the  center  of  the 
nodules,  giving  off  capillary  vessels  which  pass,  without  much 
anastomosis,  to  the  periphery  of  the  nodules,  where  they  unite  to 
form  plexuses  ;  the  capillaries  of  these  plexuses  join  to  form  the 
veins  of  the  nodules,  which  are  thus  situated  at  their  periphery. 
These  veins  unite  to  form  larger  veins,  which  leave  the  glands  at 
the  hilum  (Calvert). 

Medullated  and  nonmedullated  nerves  penetrate  the  lymph- 
glands  accompanying  the  blood-vessels  on  which  they  terminate. 

Hemolymph  Glajtds. — A  typical  lymph-gland  possesses  afferent 
and  efferent  lymph-vessels  and  a  closed  blood-vascular  system 
completely  separated  from  the  lymph-vascular  system,  as  may  have 
been  seen  from  the  foregoing  description.  Attention  has,  however, 
been  called  in  recent  years  to  certain  lymph-glands  in  which  the 
complete  separation  of  the  vascular  and  lymphatic  systems  does 
not  obtain, — glands  in  which  the  formed  elements  of  blood  and 
lymph  are  intermingled  in  the  meshes  of  the  adenoid  reticulum, 
and  which  contain  blood-sinuses  in  place  of  the  lymph-sinuses 
observed  in  the  typical  lymph-glands.  These  have  been  designated 
as  hemolymph  glands  {Blutlyinphdruseji,  hemal  glands,  hemal 
lymphatic  glands).  In  the  typical  hemolymph  glands  there  are 
no  afferent  and  efferent  lymphatic  vessels  ;  the  glands  are  inter- 
calated in  the  vascular  system.  Certain  less  clearly  defined  hemo- 
lymph glands  possess  afferent  and  efferent  lymphatics  and  blood- 
sinuses,  the  two  systems  being  not  completely  separated.  These 
may  be  considered  transitional  forms. 

Lymph-glands  with  blood-sinuses  were  first  described  by  Gibbes, 
who  found  such  glands  in  the  region  of  the  renal  artery.  They 
were  further  considered  and  more  fully  described  by  Robertson,  to 
whom  the  term  hemolymph  glands  is  to  be  credited,  and  by  Clark- 
son,  Vincent  and  Harrison,  Drummond,  Warthin,  Weidenreich 
and  Lewis.  It  appears  from  their  description  that  they  are  widely 
distributed  among  vertebrates,  although  not  equally  well  developed 


LYMPHOID    TISSUE,    LYMPH-NODULES,    AND    LYMPH-GLANDS.      20I 

in  the  different  types  studied.  Warthin  has  discussed  more  fully 
than  other  observers  the  hemolymph  glands  of  man,  and  his  account 
will  here  be  followed  in  the  main.  It  may  be  parenthetically  stated 
that  the  hemolymph  glands  are  numerous  and  well  developed  in 
the  sheep  (Warthin,  Weidenreich)  ;  not  so  well  differentiated  in  the 
dog  and  cat ;  on  the  other  hand,  well  developed  in  the  rat 
(Lewis). 

We  learn  from  the  account  of  Warthin  that  the  hemolymph 
glands  are  numerous  in  man,  in  the  prevertebral  retroperitoneal 
region,  in  the  cervical  region,  and  less  numerous  in  the  thorax. 
They  vary  in  size  from  that  of  several  millimeters  to  that  of  several 
centimeters.  They  present  a  variety  of  structure,  depending  mainly 
upon  the  arrangement  of  the  lymphoid  tissue  and  blood-sinuses. 
The  great  majority  of  these  glands  show  a  resemblance  in  structure 
to  splenic  tissue  (splenolymph  glands) ;  others  resemble  more 
closely  marrow-tissue  (marrow  lymph-glands).  Between  the  two 
varieties  of  lymph-glands  there  are  found  transition  forms,  as  also 
between  these  and  lymph-glands  (Warthin). 

The  hemolymph  glands  (splenolymph  glands)  are  surrounded 
by  a  capsule  varying  in  thickness  and  composed  of  white  fibrous 
and  elastic  tissue  and  nonstriated  muscle-cells.  From  it  trabeculae 
of  the  same  structure  pass  into  the  gland,  which  after  division  are 
lost  in  the  substance  of  the  gland.  Beneath  the  capsule  there  is 
found  a  continuous  or  discontinuous  blood-sinus,  bridged  over 
by  reticular  fibers,  from  which  anastomosing  sinuses  pass  to  the 
interior  of  the  gland.  These  blood-sinuses  are,  in  part  at  least,  Uned 
by  endothelial  cells.  The  sinuses  in  the  gland  substance  are  also 
bridged  by  trabeculae  and  reticular  fibers.  The  sinuses  divide  the 
lymphoid  tissue  into  anastomosing  masses  and  cords.  This  tissue 
consists  of  an  adenoid  reticulum,  in  the  meshes  of  which  are  found 
white  and  red  blood-cells.  The  small  lymphocytes  are  numerous; 
next  in  frequency  are  found  the  mononuclear  leucocytes  ;  transi- 
tional and  polymorphonuclear  cells.  Basophile  and  eosinophile 
cells  are  also  found.  According  to  Weidenreich,  the  eosinophile 
cells  are  numerous  ;  he  is  also  of  the  opinion  that  the  eosinophile 
granules  are  derived  from  disintegrating  red  blood-cells.  In  the 
reticulum  and  in  the  blood-sinuses  are  found  mononuclear  phago- 
cytes, the  origin  of  which  has  not  been  fully  determined.  Certain 
observers  (Schumacher,  Weidenreich)  trace  their  origin  to  the  cells 
of  the  reticulum  ;  Thoma  regards  them  as  developed  from  endo- 
thelial cells,  while  Drummond  and  others  regard  them  as  altered 
leucocytes.  They  contain  disintegrating  red  blood-cells  and  pig- 
ment (according  to  Weidenreich,  eosinophile  cells).  The  majority 
of  the  hemolymph  glands  present  a  hilum  through  which  the 
blood-vessels  enter.  The  arteries,  soon  after  entering  the  gland, 
divide  into  smaller  branches,  certain  of  which  communicate  directly 
through  blood-capillaries  with  the  blood-sinuses  (Lewis)  ;  others 
pass  to  the  adenoid  tissue.      The  larger  veins  are  in  the  trabeculae 


202  BLOOD    AND    BLOOD-FORMING    ORGANS. 

(at  the  hilum).  On  leaving  the  trabeculae  their  walls  are  formed  of 
endothelium  and  adenoid  reticulum,  which  separates  them  from  the 
blood-sinuses.  They  end  (or  begin)  in  lacunae  with  thin  walls 
which  are  perforated  and  communicate  with  the  blood-sinuses 
(Weidenreich).  Nerves  have  been  traced  to  the  hemolymph  glands 
by  Lewis  (dog,  rat).  They  probably  end  in  the  involuntary  muscle 
of  the  capsule  and  trabeculae.  Typical  hemolymph  glands  have  no 
lymph-vessels.  In  certain  glands  both  blood-  and  lymph-sinuses 
are  found.  In  such  glands  there  is  apparently  an  intermingling  of 
blood  and  lymph,  so  that  red  blood-cells  may  pass  into  the 
lymphatics. 

The  marrow  lymph-glands  are  not  so  numerous.  They  have  a 
thin  capsule  consisting  of  fibrous  tissue  but  containing  little  elastic 
and  muscular  tissue.  The  blood-sinuses  are  not  so  well  developed. 
In  the  lymphoid  tissue  the  basophile  and  eosinophile  cells  are  more 
numerous  than  in  the  splenolymph  glands,  and  large  cells  similar  to 
the  large  bone-marrow  cells  are  now  and  then  met  with. 

As  appears  from  the  accounts  of  the  majority  of  observers  who 
have  studied  hemolymph  glands,  they  have  a  hemolytic  function, 
in  that  the  red  blood-cells  are  destroyed  in  them.  Robertson  and 
Clarkson  ascribe  to  them  a  blood-forming  function.  This  has  also 
been  observed  by  Warthin  in  the  case  of  marrow  lymph -glands, 
under  certain  conditions.  The  hemolymph  glands  are  seats  of 
origin  for  the  white  blood-cells  which  appear  also  to  be  destroyed 
here  (eosinophile   cells,  Weidenreich). 


C  THE  SPLEEN. 

The  spleen  is  a  blood-forming  organ,  in  which  white  blood-cells 
and,  in  embryonic  life  and  under  certain  conditions  in  adult  life  also, 
red  blood-cells  are  formed — the  former  in  the  adenoid  tissue  (Mal- 
pighian  corpuscles)  and  spleen  pulp,  the  latter  only  in  the  spleen 
pulp. 

The  spleen  is  covered  by  peritoneum,  and  possesses  a  capsule 
consisting  of  connective  tissue,  elastic  fibers,  and  nonstriated  muscle- 
cells.  This  capsule  sends  numerous  processes  or  trabeculae  into 
the  interior  of  the  organ,  which  branch  and  form  a  framework  in 
which  the  vessels,  especially  the  veins,  are  imbedded.  This  con- 
nective-tissue framework  breaks  up  to  form  the  reticular  tissue 
which  constitutes  the  ground  substance  of  the  spleen. 

On  examining  a  section  of  the  spleen  with  the  low-power  mag- 
nifying glass,  sections  of  the  trabeculae,  and  round  or  oval  masses 
of  cells,  having  a  diameter  of  about  0.5  mm.,  and  in  structure  and 
appearance  similar  to  the  lymph-nodules  (Malpighian  corpuscles), 
are  clearly  defined  ;  between  and  around  these  structures  is  a  tissue 
rich  in  cells,  blood-vessels  and  blood-corpuscles,  known  as  the 
spleen  pulp. 


THE    SPLEEN. 


203 


The  organ  has  a  very  typical  blood  supply.  Its  arteries  enter 
at  the  hilum,  or  indented  surface,  and  its  veins  pass  out  at  the  same 
place.  On  the  penetration  of  the  vessels  through  the  capsule,  the 
latter  forms  sheaths  around  them  (trabeculse),  but  as  soon  as  the 
arteries  and  veins  separate,  the  trabecuLne  envelop  the  veins  alone. 
The  arteries  break  up  into  smaller  branches,  which  in  turn  divide 
into  a  large  number  of  tuft-like  groups  of  arterioles.  Soon  after  their 
separation  from  the  veins,  the  adventitia  (outer  fibrous  tissue  coat)  of 


j>rk 


l^^r 


^mz..^ 


Fig.  163. — Portion  of  section  of  human  spleen  ;  X  ^5-  The  figure  gives  a  general 
view  of  the  structure  of  the  spleen :  a.  Arteries  with  lymphoid  sheaths  ;  cf,  fibrous  capsule ; 
Mk,  Malpighian  corpuscle  ;  //,  spleen  pulp  ;  tr,  trabeculae  ;  v,  vein  in  trabecula  ("Atlas 
and  Epitome  of  Human  Histology,"  Sobotta). 


the  arteries  begins  to  assume  a  lymphoid  character.  This  lymphoid 
tissue  increases  here  and  there  to  form  true  lymphoid  nodules,  pos- 
sessing all  the  characteristics  already  mentioned — reticular  tissue, 
germ  centers,  etc.  These  are  the  MalpigJiian  bodies,  or  corpuscles ; 
they  are  not  very  plentifully  represented  in  man.  The  Malpighian 
bodies  with  their  germ  centers  are  formative  centers  for  the  lympho- 
cytes. The  newly  formed  cells  pass  into  the  pulp  and  mix  with  its 
elements,  which  are  then  bathed  by  the  blood  emptying  from  the 


204  BLOOD    AND    BLOOD-FORMING    ORGANS. 

arterial  capillaries  into  the  channels  of  the  pulp.  The  lymphoid 
sheaths  and  nodules  derive  their  blood  supply  from  arteries  which 
arise  from  the  lateral  branches  of  the  splenic  vessels,  and  which 
divide  into  capillaries  inside  of  the  lymph  sheaths  or  nodules,  and 
only  assume  a  venous  character  outside  of  the  lymphoid  substance. 
These  vessels  constitute  the  nutritive  vascular  system  of  the  spleen. 

The  small  arterial  branches  above  mentioned  break  up  into  very 
fine  arterioles  which  gradually  lose  their  lymphoid  sheath,  so  that 
branches  with  a  diameter  of  0.02  mm.  no  longer  possess  a  lymphoid 
sheath,  but  again  assume  an  adventitia  of  the  usual  type.  The 
smallest  arterioles  now  pass  over  into  capillaries  which  are  for  a 
time  accompanied  by  the  adventitia  (capillary  sheath),  while  the 
terminal  branches  have  the  usual  structure  of  the  capillary  wall  and 
are  gradually  lost  in  the  meshes  of  the  pulp.  (See  below.)  On  the 
other  hand,  the  beginnings  of  the  venous  capillaries  may  be  dis- 
tinctly seen  in  the  pulp  spaces.  Groups  of  these  capillaries  com- 
bine to  form  larger  vessels,  which,  however,  still  retain  a  capillary 
structure,  and  these  again  form  small  veins  which  unite  to  form  the 
larger  veins. 

F.  P.  Mall,whose  recent  contributions  on  the  structure  of  the  spleen 
have  greatly  extended  our  knowledge  of  the  microscopic  anatomy  of 
this  organ,  states  that  the  trabecular  and  vascular  systems  together 
outline  masses  of  spleen  pulp  about*  i  mm.  in  diameter,  which  he  has 
named  spleen  lobules.  Each  lobule  is  bounded  by  three  main  in- 
terlobular trabeculae,  each  of  which  sends  three  intralobular  trabe- 
culae  into  the  lobule  which  communicate  with  each  other  in  such  a 
manner  as  to  divide  the  lobule  into  about  ten  smaller  compartments. 
An  artery  enters  at  one  end  of  the  lobule  and,  passing  up 
through  its  center,  gives  off  a  branch  to  the  spleen  pulp  found  in 
each  of  the  ten  compartments  formed  by  the  intralobular  trabecular. 
The  spleen  pulp  in  these  compartments  is  arranged  in  the  form  of 
anastomosing  columns,  or  cords,  to  which  Mall  has  given  the  name 
of  pulp  cords.  The  branches  of  the  main  intralobular  artery,  going 
to  each  compartment,  divide  repeatedly  ;  the  terminal  branches 
course  in  the  spleen-pulp  cords,  and  in  their  path  give  off  numerous 
small  side  branches  which  end  in  small  expansions  known  as  the 
ampullcE  of  Thoma.  An  ampulla  of  Thoma  may  be  divided  into 
three  parts.  The  first  part,  which  is  the  ampulla  proper,  is  lined  by 
spindle-shaped  cells,  directly  continuous  with  the  endothelial  cells  of 
the  artery.  The  second  third,  which  often  communicates  with  neigh- 
boring ampullae,  contains  large  side-openings.  The  remaining  third, 
which  is  the  intermediary  segment  of  Thoma  {Thoma' s  Zwischen- 
stück), is  difficult  to  demonstrate.  It  is  bridged  over  by  fibrils  of 
reticulum,  and  its  communication  with  the  vein  is  not  wide.  The 
circulation  through  the  spleen  is  therefore  not  a  closed  one,  through 
a  system  of  capillaries  completely  closed,  but  rather  through  spaces 
in  the  spleen-pulp,  certain  of  which  are  more  direct,  leading  from 
the  terminal   arteries   to   the   veins.      According  to  this  view,  then, 


THE    SPLEEN. 


205 


"the  blood  passes  from  the  ampullfe  into  the  pulp  spaces,  then 
through  the  pores  into  the  walls  of  the  veins  to  form  columns  of 
blood  discs  which  are  pushed  from  the  smaller  to  the  larger  veins 
of  the  spleen."  The  pulp  spaces  usually  contain  veiy  (ew  blood- 
corpuscles,  in  preparations  fixed  and  prepared  in  the  usual  way, 
since  on  removal  from  the  animal  the  muscular  tissue  of  the  capsule 
and  trabeculae  contracts  and  presses  the  blood  from  pulp  spaces 
into  the  veins.  If,  however,  the  muscular  tissue  of  the  spleen  is 
paralyzed  before  the  tissue  is  fixed,  numerous  blood-corpuscles  are 
found  in  the  pulp  spaces.  In  the  above  account  of  the  ultimate 
distribution  of  the  splenic  vessels  we  have  followed  very  closel}'  the 
recent  observations  of  F.  P.  Mall.  The  accompanying  diagram 
(Fig.  164),  slightly,  though  immaterially,  modified  from  one  given 


Capsule. 

^^Y  Jy   •\^y'i'~    ^  Intralobular  venous 

,>Y      J^^  ^~     ]  spaces. 

yirTT'-  J  Intralobular  vein. 


Intralobular  trabecula.  -- 


Artery  to  one  of  the  ten 
compartments. 


Intralobular  artery. 
Interlobular  trabecula. 

Intralobular  trabecula. 
Malpighian  corpuscle. 


Ampulla  of  Thoma. 


JC       ^  1-^     — Spleen  pulp  cord. 
i''"' —         -   Interlobular  vein. 


—  Intralobular  vein. 


Fig.  164. — Diagram  of  lobule  of  the  spleen  (Mall,  '"lohns  Hopkins  Hospital 
Bulletin,"  Sept.,  Oct.,  1898).' 


by  F.  P.  Mall,  shows  clearly  the  trabecular  and  vascular  systems 
of  a  spleen  lobule.  In  larger  spleens  there  may  be  some  two  hun- 
dred thousand  of  these  lobules.  In  a  dog  weighing  10  kg.  there 
are  on  an  average  some  eighty  thousand  (F.  P.  Mall). 

The  splenic  pulp  consists  of  a  reticulum,  in  the  meshes  of 
which  are  found  (ij  fully  developed  red  blood-cells;  (2)  now 
and  then  nucleated  red  blood-cells;  (3)  in  many  animals  giant 
cells  ;  (4)  cells  containing  red  blood-corpuscles  and  the  remains  of 
such,  with  or  without  pigment  ;  (5)  the  different  varieties  of  white 
blood-cells,  especially  a  relatively  large  proportion  of  mononuclear 
leucocytes.  Pigment  granules,  either  extra-  or  intracellular,  also 
occur  in  the  splenic  pulp.  The  pigment  probably  originates  from 
disintegrating  erythrocytes.      Besides  these  are  found,  especially  in 


206 


BLOOD    AND    BLOOD-FORMING    ORGANS. 


teased  preparations,  long,  spindle-shaped  and  flat  cells,  which  are 
probably  derivatives  of  the  connective-tissue  cells  of  the  pulp  and  of 
the  endothelium  and  muscular  fibers  of  the  vessels. 


Fig.  165. — Cells  containing  pigment,  blood-corpuscles,  and  hemic  masses  from  the 
spleen  of  dog ;  X  1800  (from  cover-glass  of  H.  F.  Müller). 


_  b 


Fig.  166. — From  the  human  spleen  ;   X  8°  (chrome-silver  method)  :   a,   Larger  fibers 
of  a  Malpighian  body  ;  b,   reticular  fibrils  (Gitterfasern). 


In  embryonic  life  and  under  certain  conditions  in  postembryonic 
life  (after  severe  hemorrhage  and  in  certain  diseases)  red  blood-cells 
are  developed  in  the  spleen  pulp.      The  nucleated  red  blood-cells 


THE    BONE-MARROW.  20/ 

from  which  they  develop  may  lose  their  nuclei  in  the  spleen  pulp 
or  only  after  entering  the  circulation  (compare  Bone-marrow). 

Lymphatic  vessels  have  been  observed  in  the  capsule  and  tra- 
beculae,  but  not  in  the  spleen  pulp  nor  Malpighian  corpuscles. 

The  spleen  receives  medullated  and  nonmeduUated  nerve-fibers  ; 
the  latter  are  much  more  numerous.  The  medullated  nerve- 
fibers  are  no  doubt  the  dendrites  of  sensory  neurones.  Their 
mode  of  ending  has,  however,  not  been  determined.  It  is  probable 
that  they  will  be  found  to  terminate  in  the  fibrous-tissue  coat  of  the 
vessels,  and  in  the  trabeculae  and  capsule.  The  nonmeduUated 
nerve-fibers,  no  doubt  the  neuraxes  of  sympathetic  neurones,  are 
very  numerous  ;  they  enter  the  spleen  with  the  artery  and  mainly 
follow  its  branches.  By  means  of  the  chrome-silver  method, 
Retzius  (92)  has  shown  that  in  the  rabbit  and  mouse  these  nerve- 
fibers  follow  the  vessels,  forming  plexuses  which  surround  them, 
the  terminal  branches  of  these  plexuses  terminating  in  free  endings 
in  the  muscular  coat  of  the  arteries.  Here  and  there  a  nerve-fiber 
could  be  traced  into  the  spleen  pulp.  The  mode  of  ending  of  such 
fibers  could,  however,  not  be  determined.  The  nonstriated  muscle- 
cells  of  the  trabeculae  and  capsule  no  doubt  also  receive  their  inner- 
vation from  the  nonmeduUated  nerves  (neuraxes  of  sympathetic 
neurones). 

D,  THE  BONE-MARROW. 

The  ingrowing  periosteal  bud  which  ushers  in  the  process  of 
endochondral  ossification  constitutes  the  first  trace  of  an  embryonal 
bone-marrow  (compare  p.  117).  It  consists  mainly  of  elements 
from  the  periosteum  which  penetrate  with  the  vascular  bud  and  later 
form  the  entire  adult  bone-marrow.  The  red  bone-marrow  is  formed 
first.  This  is  present  in  embryos  and  young  animals,  and  is  devel- 
oped from  the  above  elements  during  the  process  of  ossification. 
As  Neumann  (82)  has  shown,  the  red  bone-marrow  of  the  human 
embryo  is  first  formed  in  the  bones  of  the  extremities  and  gradually 
replaced  in  a  proximal  direction,  so  that  in  the  adult  it  is  found 
only  in  the  proximal  epiphyses,  in  the  flat  bones  and  in  the 
bodies  of  the  vertebrae.  In  the  remaining  bones  and  parts  of  bones 
the  red  bone-marrow  is  replaced  by  the  yelloiv  bone-marrozu  (fat- 
marrow). 

As  a  result  of  hunger  and  certain  pathologic  conditions  the  yel- 
low bone-marrow  changes  into  a  gelatinous  substance,  which,  how- 
ever, may  again  assume  its  original  character. 

The  red  bone-marrow,  surrounded  by  a  delicate  fibrous-tissue 
membrane,  the  efidosteum,  is  a  tissue  consisting  of  various  cellu- 
lar elements  imbedded  in  a  matrix  of  reticular  tissue,  which  has 
been  demonstrated  by  Enderlen  with  the  chrome-silver  method, 
and  which  is  similar  to  the  adenoid  reticulum.  Aside  from  these 
cellular  elements,  the  marrow  contains  numerous  vessels  (see  below), 
fixed  connective-tissue  cells,  etc. 


208 


BLOOD    AND    BLOOD-FORMING    ORGANS. 


The  typical  cellular  elements  of  red  bone -marrow  are  : 
I.  The  Marrow-cells,  or  Myelocytes. — These  are  cells,  slightly 
larger  than  the  leucocytes,  possessing  a  relatively  large  nucleus  of 
round  or  oval  shape,  rarely  lobular,  containing  a  relatively  small 
amount  of  chromatin.  In  the  protoplasm  of  these  cells  are  found 
(in  man)  neutrophile  granules  and  now  and  again  small  vacuoles. 
They  are  said  to  contain  various  pigment  granules.  These  cells 
are  not  found  in  normal  blood,  but  are  found  in  circulating  blood  in 
certain  forms  of  leukemia,  where  they  may  be  distinguished  from 
the  mononuclear  leucocytes  partly  by  their  structure,  more  particu- 


Fig.  167. — Cover-glass  preparation  from  the  bone-marrow  of  dog ;  X  1200  (from 
preparation  of  H.  F.  Müller)  :  a.  Mast-cell  ;  b,  lymphocyte  ;  c,  eosinophile  cell ;  d,  red 
blood-cell  ;  e,  erythroblast  in  process  of  division  ;  f,  f,  normoblast ;  g,  erythroblast. 
Myelocyte  not  shown  in  this  figure. 


larly   by   the  presence   of  neutrophile   granules   not  found  in  the 
mononuclear  leucocytes. 

2.  Nucleated  Red  Blood-cells  containing  Hemoglobin. — Two 
varieties  of  these  cells  are  recognized  structurally,  with  interme- 
diary stages,  as  one  variety  is  developed  from  the  other.  The 
erythroblasts,  being  genetically  the  earlier  cells,  possess  relatively 
large  nuclei  with  distinct  chromatin  network,  surrounded  by  a 
protoplasm  tinged  with  hemoglobin,  and  are  often  found  in  a  stage 
of  mitosis.  The  other  variety  of  nucleated  red  blood-cells,  the 
normoblasts,  are  developed  from  the  erythroblasts.  They  contain 
globular  nuclei,  staining  deeply,  in  which  no  chromatin  network 
is  recognizable,  and  surrounded  by  a  layer  of  protoplasm  containing 
hemoglobin.  The  normoblasts  are  changed  into  the  nonnucleated 
red  blood-discs  by  the  extrusion  of  the  nucleus.  This  process 
occurs  normally  in  the  red  bone-tnarrow,  or  in  the  venous  spaces 


THE    BONE-MARROW. 


209 


of  the  bone-marrow  (see  below).      In  certain  pathologic  conditions, 
nucleated  red  blood-cells  are  found  in  the  circulation, 

3.  Cells  with  Eosinophile  Gramdcs. — In  the  red  bone-marrow 
are  found  numerous  eosinophile  (acidophile)  cells,  some  with  round 
or  oval  nuclei  (mononuclear  eosinophile  cells),  others  with  horse- 
shoe-shaped nuclei  (transitional  eosinophile  cells),  and  still  others 
with  polymorphous  nuclei.  The  latter,  which  are  the  most  numer- 
ous, are  no  doubt  the  mature  cells,  and  are  identical  with  those 
elements  of  the  blood  having;  the  same  structure. 


Fig.  168. — From  a  section  through  human  red  bone-marrow  ;  X  680.  Technic 
No.  216  :  a,  f.  Normoblasts  ;  b,  reticulum  ;  c,  mitosis  in  giant  cell ;  d,  giant  cell ;  e,  h, 
myelocytes  ;  g,  mitosis  ;   i,  space  containing  fat-cells. 


4.  Cells  with  basophilic  granules.  In  the  bone-marrow  are  found 
mononuclear  cells  in  which  basophile  granules  may  be  differentiated 
with  special  reagents. 

5.  The  various  forms  of  lejicocytes  and  the  lymphocytes  found  in 
blood  and  lymph. 

6.  The  giant  cells  (myeloplaxes),  which  are  situated  in  the  center 
of  the  marrow,  and  contain  simple  or  polymorphous  nuclei,  or 
lie  adjacent  to  the  bone  in  the  form  of  osteoclasts,  which  are,  as  a 
rule,  polynuclear  (compare  p.  120).  The  physiologic  significance 
of  the  giant  cells  is  still  obscure.  They  probably  originate  from 
single  leucocytes  by  an  increase  in  size  of  the  latter,  and  not,  as 
many  assume,  from  a  fusing  of  several  leucocytes.  The  giant  cells 
are  endowed  with  ameboid  movement,  and  often  act  as  phagocytes 
(the  latter  quality  is  denied  them  by  M.  Heidenhain,  94). 

14 


2IO  BLOOD  AND  BLOOD-FORMING  ORGANS. 

M.  Heidenhain  (94)  has  made  a  particular  study  of  the  giant 
cells.  According  to  him  the  nuclei  of  these  cells  take  the  form  of  per- 
forated hollow  spheres  whose  thick  walls  contain  "endoplasm."  The 
latter  is  continuous  with  the  remaining  protoplasm  of  the  cell,  the  "  exo- 
plasm  "  through  the  "perforating  canals"  of  the  nuclear  wall.  The 
exoplasm  is  arranged  in  three  concentric  layers,  separated  from  each 
other  by  membranes,  the  external  membrane  of  the  outer  zone  being  the 
membrane  of  the  cell.  The  outer  layer  or  marginal  zone  is  of  a  transient 
nature,  but  is  always  renewed  by  the  cell.  Thus,  the  cell-membrane  is 
replaced  by  the  secondary  membrane  situated  between  the  second  and 
third  zone.  According  to  the  same  author  the  functions  of  the  giant 
cells  appear  to  consist  in  ' '  the  selection  and  elaboration  of  certain  albu- 
minoid substances  of  the  lymph  and  blood  currents,  which  are  later 
returned  to  the  circulation."  The  number  of  centrosomes  occurring  in 
the  mononuclear  giant  cells  of  the  bone-marrow  is  very  large,  and  in 
some  cases,  as  in  a  pluripolar  mitosis,  may  even  exceed  one  hundred  in 
number. 

The  distribution  of  the  blood-vessels  in  the  bone-marrow  is  as 
follows  :  On  entering  the  bone  the  nutrient  arteries  divide  into  a 
large  number  of  small  branches,  which  then  break  up  into  small 
arterial  capillaries.  The  latter  pass  over  into  relatively  large  venous 
capillaries  with  relatively  thin  walls,  which  appear  perforated  in 
certain  places,  so  that  the  venous  blood  pours  into  the  spaces 
of  the  red  bone-marrow  where  the  current  is  very  slow.  The 
blood  passes  out  by  means  of  smaller  veins  formed  by  the  conflu- 
ence of  the  capillaries  which  collect  the  blood  from  the  marrow.  It 
is  worth  mentioning  that  the  venous  vessels,  while  inside  of  the 
bone-marrow,  possess  no  valves  ;  but,  on  the  other  hand,  they 
have  an  unusually  large  number  of  valves  immediately  after  leaving 
the  bone. 

Yellow  bone-marrow  is  derived  from  red  bone-marrow  by  a 
change  of  the  marrow-cells  into  fat-cells.  The  gelatinous  marrow, 
on  the  contrary,  is  characterized  by  the  small  quantity  of  fat  which 
it  contains.  Neither  the  yellow  nor  the  gelatinous  bone-marrow  is 
a  blood-forming  organ  (compare  Neumann,  90;  Bizzozero,  91  ; 
H.  F.  Müller,  91  ;  van  der  Stricht,  92). 


E.  THE  THYMUS  GLAND. 

The  thymus  gland  is  usually  considered  as  belonging  to  the 
lymphoid  organs,  although  in  its  earliest  development  it  resembles 
an  epithelial,  glandular  structure.  In  the  epithelial  stage,  this  gland 
develops  from  the  entoderm  of  the  second  and  third  gill  clefts. 
Mesodermic  cells  grow  into  this  epithelial  structure,  proliferate  and 
then  differentiate  into  a  tissue  resembling  adenoid  tissue.  It  retains 
this  structure  until  about  the  end  of  the  second  year  after  birth,  when 
it  slowly  begins  to  retrograde  into  a  mass  of  fibrous  tissue,  adipose 
tissue,  and  cellular  debris,  which  structure  it  presents  in  adult  life. 


THE   THYMUS    GLAND.  2  1  I 

By  means  of  connective-tissue  septa,  the  thymus  is  divided  into 
larger  lobes,  and  these  again  into  smaller  lobes,  until  finally  a 
number  of  small,  irregularly  spheric  structures  are  formed — the 
lobules  of  the  gland.  These  are,  however,  connected  by  cords  of 
lymphoid  tissue,  the  so-called  medullary  cords.      The  lobules  of  the 

*       '^    ''  ''-^-^^^^^^ 

a 


l,_exi_-~  , _  ^ 


■c< 


Fig.  169. — A  small  lobule  fiom  the  thymus  of  child,  with  well  developed  cortex, 
presenting  a  structure  'similar  to  thit  of  the  cortex  of  a  lymph  gland  ,  X  60  :  a, 
Hilus  ;   b,  medullary  substance  ;    c,  cortical  substance  ;   d,  trabecula. 

thymus  gland  consist  of  a  reticular  connective  tissue  much  more  deli- 
cate at  the  periphery  than  at  the  center  of  the  lobule.  The  reticulum 
supports  branched  connective-tissue  cells,  with  relatively  large  nuclei. 
In  the  meshes  of  the  reticular  tissue  are  cellular  elements,  in  structure 
similar  to  the  lymphocytes,  which  are  more  numerous  at  the  periph- 
ery of  the  lobule  than  at  its  center,  so  that  we  may  here  speak  of 


Fig.    170. — Hassal's   corpuscle   and  a  small  portion  of  medullary  substance,  showing 
reticulum  and  cells,  from  thymus  of  a  child  ten  days  old. 

the  lobule  as  divided  into  a  cortical  and  a  medullary  portion. 
Leucocytes  with  polymorphous  nuclei,  also  leucocytes  with  eosino- 
phile granules,  are  also  found.  The  medullary  portion  is  usually 
entirely  surrounded  by  the  cortical  substance,  but  may  penetrate  to 
the  periphery  of  the  lobule,  allowing  the  blood-vessels  to  enter  and 


212  BLOOD    AND    BLOOD-FORMING    ORGANS. 

leave  at  this  point.  In  the  cortical  substance  occur  changes  which 
result  in  the  formation  of  structures  closely  resembling  the  cortical 
nodules  of  lymph-glands. 

Until  recently,  little  was  known  of  the  significance  of  this  organ. 
A  careful  study  revealed  a  similarity  between  certain  cellular  ele- 
ments of  the  thymus  and  the  constituents  of  the  blood-forming 
organs, — a  similarity  still  more  striking  from  the  presence  of 
nucleated  red  blood-cells  in  the  thymus.  Logically,  then,  the 
embryonal  thymus  is  to  be  regarded  as  one  of  the  blood-forming 
organs  (Schaffer,  93,  I). 

During  embryonic  life  from  the  fourth  month  on  and  for  some 
time  after  birth,  there  are  found  in  the  thymus  peculiar  epithelial 
bodies,  known  as  the  corpuscles  of  Hassal.  They  are  spheric  struc- 
tures, about  o.  I  mm.  in  diameter,  whose  periphery  shows  a  con- 
centric arrangement  of  the  epithelial  cells.  In  their  central  portions 
are  found  a  few  nuclear  and  cellular  fragments.  These  bodies 
occur  only  in  the  thymus  gland.  They  are  remnants  of  the  primary 
epithelial,  glandular  structure  of  the  thymus,  and  are  formed  by  an 
ingrowth  of  mesoderm  which  breaks  down  the  epithelium  into  small 
irregular  masses,  mechanically  compressed  by  the  proliferating 
mesoderm. 

The  thymus  gland  has  a  relatively  rich  blood  supply.  Arterial 
branches  enter  the  lobules  usually  near  the  medullary  cords  and  form 
capillary  networks  at  the  boundaries  of  the  medullary  and  cortical 
portions  ;  from  this  anastomosing  capillaries  radiate  to  the  peripheiy 
of  the  lobules,  joining  to  form  a  relatively  dense  capillary  network 
under  the  connective-tissue  covering.  The  veins  arise  from  this  cap- 
illary network  and  are  situated  mostly  in  the  interlobular  connec- 
tive tissue.  Certain  of  the  veins  are  in  the  medullary  portions  of 
the  lobules,  where  they  accompany  the  arteries  (Kölliker,  v.  Ebner). 

The  lymph-vessels  are  in  the  interlobular  connective  tissue  in 
close  apposition  with  the  adenoid  tissue. 

Nerve-fibers  accompanying  the  blood-vessels  have  been  ob- 
served. 


IL  THE  CIRCULATORY  SYSTEM. 

The  walls  of  the  blood-vessels  vary  'in  structure  in  the  different 
divisions  of  the  vascular  system.  All  the  vessels,  including  the 
heart,  possess  an  inner  endothelial  lining.  In  addition  to  this,  the 
larger  vessels  are  provided  with  other  layers,  which  consist,  on  the 
one  hand,  of  connective  and  elastic  tissue  and,  on  the  other,  of  non- 
striated  muscle-fibers.  The  vessels  are  also  richly  supplied  with 
nerves,  that  form  plexuses  in  which  ganglion  cells  are  sometimes 
found,  and  in  the  larger  vessels  the  outer  layer  is  honeycombed  by 
nutrient  blood-vessels,  called  vasa  vasorum.  In  the  heart,  the  mus- 
cular tissue  is  especially  well  developed.    According  to  the  structure 


THE    VASCULAR    SYSTEM.  21  3 

of  the  vessels,  we  distinguish,  in  both  arteries  and  veins,  large, 
medium-sized,  small,  and  precapillary  vessels,  and  finally,  the  capil- 
laries themselves.  The  latter  connect  the  arterial  and  venous  pre- 
capillary vessels.  In  the  lymphatic  system  we  must  further  dis- 
tinguish between  the  larger  lymph-vessels,  the  sinuses,  and  the 
capillaries. 

A.  THE  VASCULAR  SYSTEM. 

U  THE  HEART. 

In  the  heart  there  are  recognized  three  main  coats — the  endo- 
cardium, the  myocardium,  and  the  pericardium  or  epicardium. 

The  cndocardiuni  consists  of  plate-like  endothelial  cells,  with 
very  irregular  outlines.  Beneath  this  endothelial  layer  is  a  thin 
membrane  composed  of  unstriped  muscle-cells,  together  with  a 
small  number  of  connective-tissue  and  elastic  fibers.  Below  this  is 
a  somewhat  thicker  and  looser  layer  of  elastic  tissue  connected  ex- 
ternally with  the  myocardium.  Between  the  two  layers  are  found, 
here  and  there,  traces  of  a  layer  of  Ptirkinje' s  fibers  (compare  p. 
147).  Purkinje' s  fibers  are  found  in  the  heart  of  many  mammalia, 
although  absent  in  the  heart  of  the  human  adult. 

The  aiLvicidoventricular  valves  of  the  heart  represent,  in  general, 
a  duplication  of  the  endocardium.  The  layer  of  smooth  muscle- 
fibers  found  in  the  latter  is  better  developed  on  the  auricular  surface. 
At  the  points  of  insertion  of  the  chordae  tendineae  the  connective- 
tissue  layer  is  strongly  developed  and  assumes  a  tendon-like  con- 
sistency. The  semihinar  valves  of  the  aorta  and  pulmonary  artery 
have  a  similar  structure.  In  the  nodules  of  these  valves  the  elastic 
fibers  are  especially  dense  in  their  arrangement. 

The  niyocardiiun  is  made  up  of  the  heart  muscle-fibers  already 
described  {via.  p.  145).  Between  the  heart  muscle- fibers  and 
bundles  of  such  fibers  are  thin  layers  of  fibrous  connective  tissue 
containing  a  network  of  capillaries.  The  myocardium  of  the  auricles 
may  be  divided  into  two  layers,  of  which  the  outer  is  common  to  both 
auricles,  the  fibers  of  which  have  a  nearly  circular  arrangement,  while 
the  deeper  layer  is  separate  for  each  chamber.  The  arrange- 
ment of  the  heart  muscle-fibers  of  the  ventricles  is  complicated. 
With  special  methods  of  maceration  J.  B.  MacCallum  was  able  to 
show  that  "the  superficial  fibers  are  found  to  have  origin  in  the 
auriculoventricular  ring,  to  wind  about  the  heart  spirally,  and  to  end 
in  tendons  of  the  papillary  muscle  of  the  opposite  ventricle.  The 
deep  layers  also  begin  in  the  tendon  of  one  auriculoventricular  ring, 
pass  around  to  the  interventricular  septum,  cross  over  backward  or 
forward  in  this  septum,  and  end  in  the  papillary  muscle  of  the  other 
ventricle.  In  the  light  of  this,  the  heart  consists  of  several  bands 
of  muscles  with  tendons  at  each  end,  rolled  up  like  a  scroll  or  like 
the  letter  S."      The  musculature  of  the  auricles  is  almost  completely 


214  THE    CIRCULATORY    SYSTEM. 

separated  from  that  of  the  ventricles  by  means  of  the  annulus  fibro- 
sus  atrioventricularis ,  or  the  auriculoventricular  ring,  which  consists 
in  the  adult  of  connective  tissue  containing  numerous  delicate  and 
densely  interwoven  elastic  fibers. 

The  pericardium  consists  of  a  visceral  layer,  the  epicardium,  ad- 
hering closely  to  the  myocardium,  and  a  parietal  layer  (pericardium), 
loosely  surrounding  the  heart  and  continuous  at  the  upper  portion 
of  the  heart  with  the  visceral  layer.  Between  the  two  layers  is  the 
pericardial  cavity,  containing  a  small  quantity  of  a  serous  fluid — 
the  pericardial  fluid.  In  the  visceral  layer  (the  epicardium)  we 
find  a  connective-tissue  stroma  covered  by  flattened  mesothelial 
cells.  A  similar  structure  occurs  also  in  the  parietal  layer,  although 
here  the  connective -tissue  stroma  is  considerably  reinforced.  De- 
posits of  fat,  in  most  cases  in  the  neighborhood  of  the  blood-vessels, 
are  sometimes  seen  between  the  myocardium  and  the  visceral  layer 
of  the  pericardium. 

According  to  Seipp,  the  distribution  of  the  elastic  tissue  in  the 
heart  is  as  follows  :  The  endocardium  of  the  ventricles  contains  far 
more  elastic  tissue  than  that  of  the  auricles,  especially  in  the 
left  ventricle,  where  even  fenestrated  membranes  may  be  present. 
In  the  myocardium  of  the  ventricles  there  are  no  elastic  fibers  aside 
from  those  which  are  found  in  the  adventitia  of  the  contained  blood- 
vessels. In  the  myocardium  of  the  auricles,  on  the  contrary,  such 
fibers  are  very  numerous  and  are  continuous  with  the  elastic 
elements  in  the  walls  of  the  great  veins.  The  epicardium  also  pre- 
sents elastic  fibers  in  the  auricles  continuous  with  those  of  the  great 
veins  emptying  into  the  heart,  and  in  the  ventricles  continuous  with 
those  in  the  adventitia  of  the  conus  arteriosus.  In  those  portions 
of  the  heart-wall  containing  no  muscular  tissue  the  elastic  elements 
of  the  epicardium  are  continuous  with  those  of  the  endocardium.  In 
the  new-born  the  cardiac  valves  possess  no  elastic  fibers,  although 
they  are  present  in  the  adult.  They  are  developed  on  that  side  of 
each  valve,  which,  on  closing,  is  the  more  stretched — for  instance, 
on  the  auricular  side  of  the  auriculoventricular  valves. 

The  heart  has  a  rich  blood  supply.  The  capillaries  of  the  myo- 
cardium are  very  numerous,  and  so  closely  placed  around  the 
muscle  bundles  that  each  muscular  fiber  comes  in  contact  with  one 
or  more  capillaries.  In  the  endocardium  the  vessels  are  confined 
to  the  connective  tissue.  The  auriculoventricular  valves  con- 
tain blood-vessels,  in  contradistinction  to  the  semilunar  valves, 
which  are  non-vascular,  while  the  chordae  tendinese  are  at  best  very 
poorly  supplied  with  capillaries. 

The  coronary  arteries,  which  terminate  in  the  capillaries  above 
mentioned,  are  terminal  arteries  in  the  sense  that  "  the  resistance  in 
the  anastomosing  branches  is  greater  than  the  blood  pressure  in  the 
arteries  leading  to  those  branches  (Pratt,  98).  This  observer  has 
further  shown  that  the  vessels  of  Thebesius  (small  veins  which 
open  on  the  endocardial  surfaces  of  the  ventricles  and  auricles  and 


THE    VASCULAR    SYSTEM.  2  I  5 

communicate  directly  with  all  the  chambers  of  the  heart)  "open 
from  the  ventricles  and  auricles  into  a  system  of  fine  branches  that 
communicate  with  the  coronary  arteries  and  veins  by  means  of 
capillaries,  and  with  the  veins,  but  not  with  the  arteries,  by  passages 
of  somewhat  larger  size";  so  that,  although  the  blood  supply  through 
the  coronary  arteries  for  a  given  area  of  the  myocardium  is  cut  off, 
the  heart  muscle  of  this  area  may  receive  blood  through  the  vessels 
of  Thebesius. 

Lymphatic  nehvoi^ks  have  been  shown  to  exist  in  the  endocar- 
dium, and  their  presence  in  the  pericardium  is  not  difficult  to  demon- 
strate. Little  is  known  with  regard  to  the  lymph-channels  of  the 
myocardium. 

The  nerve  supply  of  the   heart  includes  numerous  medullated 
nerve-fibers,  the  dendrites  of  sensory  neurones,  and  numerous  non- 
medullated  fibers,  the  neuraxes  of  sympathetic  neurones.     Smirnow 
(95)  described  sensory  nerve-endings  in  the  endocardium  of  amphibia 
and  mammalia,  which  he  suggests  may  be  the  terminations  of  the 
depressor  nerve.     Dogiel  (98)  has  corroborated  and  extended  these 
observations,    and   has  described    complicated   sensory  telodendria 
situated  both  in  the  endo-  and  pericardium.      The  latter  states  that, 
after  forming  plexuses  and  undergoing  repeated  division,  the  medul- 
lated sensory  nerves    lose   their  medullary  sheaths,   the  neuraxes 
further   dividing  in  numerous  varicose  fibers,  variously  interwoven 
and   terminating  in  telodendria,  which  vary  greatly  in   shape  and 
configuration.     These  telodendria   are  surrounded   by  a   granular 
substance   containing  branched    cells,    probably    connective-tissue 
cells,  the  interlacing  branches   of  which  form  a  framework  for  the 
telodendria.      Similar  sensory  nerve-endings  occur  in  the  adventitia 
of  the   arteries  and   veins   of  the   pericardium    (Dogiel,   98)  ;    and 
Schemetkin  has  shown  that  sensory  nerve-endings  occur  in  the  adven- 
titia and  intima,  especially  in  the  latter,  of  the  arch  of  the  aorta  and 
pulmonary  arteries.     In  the   heart,  under  the  pericardium   on  the 
posterior  wall  of  the  auricles  and  in  the  sulcus  coronarius,  are  found 
numerous   sympathetic    neurones   whose   cell-bodies    are   grouped 
to  form  sympathetic  ganglia.      The  neuraxes  of  these  sympathetic 
neurones — varicose,     nonmedullated     nerve-fibers — form    intricate 
plexuses  situated  under  the  pericardium  and,  penetrating  the  myo- 
cardium, surround  the  bundles  of  heart  muscle-fibers.      From  the 
varicose  nerve-fibers  constituting  these  plexuses,  fine  branches  are 
given  off,  which   terminate   on  the   heart  muscle-cells  in  a  manner 
previously  described  (see  p.  166  and  Fig.  132).      The  cell-bodies  of 
the  sympathetic  neurones,  the   neuraxes  of  which  thus  terminate 
on  the   heart   muscle-fibers,    are  surrounded  by   end-baskets,  the 
telodendria  of  small  medullated  nerve-fibers  which  reach  the  heart 
through  the  vagi.     The  slowed  and  otherwise  altered  action  of  the 
heart-muscle,  produced   on   stimulating  directly   or    indirectly  the 
vagus  nerves  is  therefore  due  not  to  a  direct  action  of  these  nerve- 
fibers  on  the  heart  muscle-cells,  but  to  an  altered  functional  activity 


2l6  THE    CIRCULATORY    SYSTEM. 

produced  by  vagus  stimuli  in  at  least  some  of  the  sympathetic  neu- 
rones situated  in  the  heart,  the  neuraxes  of  which  convey  the  im- 
pulse to  the  heart  muscle.  The  heart  receives  further  nerve  supply 
through  sympathetic  neurones,  the  cell-bodies  of  which  are  situated 
in  the  inferior  cervical  and  stellate  ganglia,  the  neuraxes  of  which 
enter  the  heart  as  the  augmentor  or  accelerator  nerves  of  the  heart. 
The  mode  of  ending  of  these  nerve-fibers  has  not  as  yet  been  fully 
determined.  It  may  be  suggested  as  quite  probable  that  they  ter- 
minate on  the  dendrites  of  sympathetic  neurones,  the  cell-bodies  of 
which  are  not  inclosed  by  end-baskets  of  nerves  reaching  the  heart 
through  the  vagi,  as  above  described.  It  is  also  possible  that  they 
end  directly  on  the  heart  muscle-cells.  The  cell-bodies  of  the 
sympathetic  neurones,  the  neuraxes  of  which  form  the  augmentor 
nerves,  are  surrounded  by  the  telodendria  of  small  medullated 
fibers,  forming  end-baskets,  which  leave  the  spinal  cord  through  the 
anterior  roots  of  the  upper  dorsal  nerves.  Besides  the  nerves  here 
described,  nonmedullated  nerves  (whether  the  neuraxes  of  sympa- 
thetic neurones,  the  cell-bodies  of  which  are  situated  inside  or  out- 
side of  the  heart  has  not  been  fully  determined),  form  plexuses  in 
the  walls  of  the  coronary  vessels,  terminating,  it  would  seem,  on  the 
muscle-cells  of  the  media  (vasomotor  nerves). 


2.  THE  BLOOD-VESSELS. 

A  cross-section  of  a  blood-vessel  shows  several  coats.  The 
inner  consists  of  flattened  endothelial  cells,  and  is  common  to  all 
vessels.  The  second  varies  greatly  in  thickness,  contains  most  of 
the  contractile  elements  of  the  arterial  wall,  and  is  known  as  the 
media,  or  tunica  media.  Its  elastic  fibers  have  in  general  a  circular 
arrangement  and  are  fused  at  the  inner  and  outer  surfaces  to  form 
fenestrated  membranes,  the  lamina  elastica  interna  and  externa. 
Outside  of  the  media  lies  the  adventitia  or  tunica  externa,  consist- 
ing in  the  arteries  almost  entirely  of  connective  tissue  and  in  the 
veins  principally  of  contractile  elements,  smooth  muscle-fibers. 
Between  the  internal  elastic  membrane  and  the  endothelial  layer  is 
a  fibrous  stratum  which  varies  in  structure  in  the  different  vessels 
of  larger  caliber.  This  is  the  subendothelial  layer,  or  the  inner 
fibrous  layer,  and  forms,  together  with  the  endothelium,  the  intima 
or  tunica  intima.  Bonnet  (96),  as  a  result  of  his  own  investigations, 
suggests  a  somewhat  different  classification  of  the  layers  composing 
the  arterial  wall.  According  to  him,  the  endothelium  alone  con- 
stitutes the  intima.  The  elastic  membranes,  both  internal  and 
external,  together  with  the  tissue  lying  between  them,  and  that 
between  the  internal  elastic  membrane  and  the  intima,  constitute 
the  media.  The  tissue  layers  outside  the  external  elastic  membrane 
form  the  tunica  externa  (adventitia). 

{a)  Arteries. — In  \hQ  great  arterial  trunks,  such  as  the  pulmo- 
nalis,  carotis,  iliaca,  etc.,  the  tunica  media  possesses  a  very  typical 


THE    VASCULAR    SYSTEM.  21/ 

Structure.      It  is   divided  by  means  of  elastic  fibers  and  membranes 


y    Intima. 

,,_         Elastica  in- 
ifM^^y  terna. 


■^   Endothelium  of 
the  intima. 


^  >     Media. 


Fenestrated 
elastic    mem- 
brane. 

Elastica  ex- 
terna. 

Inner  laj-er  of 
adventitia. 


Outer  layer  of 

adventitia. 
Vasa  vasorum. 


Fig.  171. — Cross-section  of  the  human  carotid  artery  ;    X  'SO- 

(fenestrated  membranes)  into  a  large  number  of  concentric  layers 
containing  but  few  muscle-fibers.  Here  also  the  tunica  media  is 
separated  from  the  intima  by  an  elastic  limiting  membrane,  the 
fenestrated  membrane  of  Henle,  or  the  lamina  elastica  interna.  In 
the  aorta  this  membrane  as  such  is  not  recognizable.  The  intima 
presents  three  distinct  layers — the  inner  composed  of  flattened  endo- 
thelial cells,  and  the  other  two  consisting  chiefly  of  elastic  tissue 
(fibrous  layers).      Of  these  latter  the  inner  is  the  richer  in  cellular 


Endothelium  of  the 

intima. 
■Intima. 

Media. 


Adventitia  with 
nonstriated    mus- 
cle-fibers in  cross- 
section. 


Fig.  172. — Section  through  human  artery,  one  of  the  smaller  of  the  medium-sized  ;  >(  640. 

elements  and  has  a  longitudinal  arrangement  of  its  fibers,  while  the 


2l8  THE    CIRCULATORY    SYSTEM. 

outer  is  the  looser  in  structure,  possesses  few  cellular  elements,  and 
shows  a  circular  arrangement  of  its  fibers.  The  adventitia  is  also 
made  up  of  fibro-elastic  tissue,  but  in  this  case  with  a  still  looser 
structure  and  a  longitudinal  arrangement  of  its  elastic  fibers.  In  the 
outer  portion  of  the  adventitia  the  white  fibrous  tissue  is  more 
abundant.      The  adventitia  is  rich  in  blood-vessels. 

The  medium-sized  arteries  differ  in  structure  from  the  larger  in 

that  the  elastic  elements  of  the 
intima  and  media  are  replaced  to 
a  considerable  extent  by  nonstri- 
ated  muscular  fibers.  To  this  type 
belong  the  majority  of  the  arterial 
vessels,  ranging  in  caliber  from  the 
brachial,  crural,  and  radial  arteries 
to  the  supraorbital  artery.  In 
these  the  intima  shows,  besides  its 
endothelium,  only  a  single  connec- 
tive-tissue layer  with  numerous 
Fig.  173.— Precapillary  vessels  from     longitudinal    fibers,  the   subendo- 

mesentery  of  cat :  a.  Precapillary  artery  ;  thelial  layer,  which  is  thin  and  IS 
(5,  precapillary  vein  possessing  no  muscu-       1.      •,      ,  .  ,1       1  ,1         r 

lar  tissue.  limited    externally  by    the   tenes- 

trated  membrane  of  Henle  (lamina 
elastica  interna).  The  media  no  longer  gives  the  impression  of 
being  laminated,  but  consists  of  circularly  arranged  muscle-fibers 
separated  from  each  other  by  elastic  fibers  and  membranes  and  a 
small  amount  of  fibrous  connective  tissue  in  such  a  way  that  the 
muscle-cells  form  more  or  less  clearly  defined  groups.  Here  also 
the  media  is  limited  externally  by  the  external  elastic  membrane. 
The  adventitia,  which  becomes  looser  externally,  is  not  so  well  de- 
veloped as  in  the  larger  vessels,  but  presents  in  general  the  same 
structure.  In  certain  arteries  (renal,  splenic,  dorsalis  penis)  it  shows 
in  its  inner  layers  scattered  longitudinal  muscle-cells,  which,  how- 
ever, may  also  occur  in  other  arteries  at  their  points  of  division. 

With  regard  to  the  elastic  tissues,  the  arteries  of  the  brain  differ 
to  some  extent  from  those  of  the  remainder  of  the  body.  The 
elastica  interna  is  much  more  prominent,  the  elastic  fibers  in  the 
circular  muscular  layer  are  fewer,  and  the  longitudinal  strands  are 
almost  entirely  lacking  (H.  Triepel). 

The  walls  of  the  smaller  arteries  consist  mainly  of  the  circular 
muscular  layer  of  the  media.  The  intima  is  reduced  to  the  endo- 
thelium, which  rests  directly  on  the  elastic  internal  limiting  mem- 
brane. Outside  of  the  external  limiting  membrane  is  the  adventitia, 
which  now  consists  of  a  small  quantity  of  connective  tissue.  The 
vasa  vasorum  have  disappeared.  To  this  type  belong  the  supra- 
orbital, central  artery  of  the  retina,  etc. 

In  the  so-called  precapillary  vessels  the  intima  consists  only 
of  the  endothelial  layer.  The  internal  elastic  membrane  is  very 
delicate.      The  media  no  longer  forms  a  continuous  layer,  but  is 


THE    VASCULAR    SYSTEM. 


219 


made  up  of  a  few  circularly  disposed  muscular  fibers.  The  adven- 
titia  is  composed  of  a  small  quantity  of  connective  tissue,  and  con- 
tains no  vasa  vasorum. 

(p)  Veins. — In  the  foregoing  account  of  the  structure  of  the 
arteries  we  have  described  the  structure  of  their  walls  according  to 
the  caliber  of  the  vessels.  Such  a  differentiation  in  the  case  of  the 
veins  would  be  impossible,  since  sometimes  veins  of  the  same  cali- 
ber present  decided  differences  in  structure  in  various  parts  of  the 
body. 

For  the  sake  of  convenience,  we  will  commence  with  the  de- 
scription of  a  vein  of  medium  size.  Its  intima  consists  of  three 
layers  :  (i)  Of  an  inner  layer  of  endothelium  ;  (2)  of  an  underly- 
ing layer  of  muscle-cells,  interrupted  here  and  there  by  connective 
tissue  ;  and  (3)  of  a  fibrous  connective -tissue  layer  containing  fewer 
elastic  but  more  white  fibrous  connective -tissue  fibers  than  is  the 
case  in  the  arteries.     Externally,  the  intima  is  limited  by  an  in- 


.'•Intima. 

\"  Elastica  interna. 


Blood-    -I'^ti^j&ou     „ 
vessel.    ,i  "  .-  '^ 


V  Media. 


Fenestrated  elastic 
membrane. 


Inner  layer  of  the 
adventitia  with 
longitudinally  ar- 
ranged muscle- 
cells. 


Connective  tissue 
of  the  adventitia. 


Nerve. 


Fig.  174. — Cross-section  of  human  internal  jugular  vein.      At  the  left  of  the  nerve  are 
two  large  blood-vessels  with  a  smaller  one  between  them  (vasa, vasorum)  ;    X  ^SO- 


ternal  elastic  layer.  The  media  is  in  general  less  highly  developed 
than  that  of  a  corresponding  artery,  and  contains  muscle-cells  which 
have  a  circular  arrangement  and  in  some  veins  form  a  continuous 


220  THE    CIRCULATORY    SYSTEM. 

layer,  although  they  sometimes  occur  as  isolated  fibers.  The  adven- 
titia  shows  an  inner  longitudinal  muscular  layer,  which  may  be  quite 
prominent  and  even  form  the  bulk  of  the  muscular  tissue  in  the  wall 
of  the  vein.  Otherwise  the  adventitia  of  the  veins  belonging  to  this 
class  corresponds  in  general  to  that  of  the  arteries  of  the  same 
size  ;  but  here  also  we  have,  as  in  the  intima,  a  preponderance  of 
white  fibrous  connective-tissue  elements. 

In  the  crural,  brachial,  and  subcutaneous  veins,  the  muscula- 
ture of  the  media  is  prominent ;  while  in  the  jugular,  subclavian, 
and  innominate  veins,  and  in  those  of  the  dura  and  pia  mater,  the 
muscular  tissue  of  the  media  is  entirely  wanting,  and,  as  a  conse- 
quence, the  adventitia  with  its  musculature,  if  present,  is  joined 
directly  to  the  intima. 

In  the  smaller  veins  the  vascular  wall  is  reduced  to  an  endothe- 
lial lining,  an  internal  elastic  membrane,  a  media  consisting  of 
interrupted  circular  bands  of  smooth  muscle-fibers  (which  may  be 
absent),  and  an  adventitia  containing  a  few  muscle-fibers.  The 
precapillary  veins,  which  possess  in  general  thinner  walls  than  the 
corresponding  arteries,  present  a  greatly  reduced  intima  and  ad- 
ventitia, while  the  media  has  completely  disappeared. 

Intima. 
Media. 


—  Adventitia  with 
nonstriated 
muscle-cells 
in  cross-sec- 
tions. 


Fig.  175. — Section  of  small  vein  (human);  X  64°' 

The  valves  of  the  veins  are  reduplications  of  the  intima  and 
vary  slightly  in  structure  at  their  two  surfaces.  The  inner  surface 
next  to  the  blood  current  is  covered  by  elongated  endothelial  cells, 
while  the  outer  surface  possesses  an  endothelial  lining  composed  of 
much  shorter  cellular  elements.  The  greater  part  of  the  valvular 
structure  consists  of  white  fibrous  connective-tissue  and  elastic  fibers. 
Flattened  and  circularly  arranged  muscle-cells  are  met  with  at  the 
inner  surface  of  many  of  the  larger  valves.  The  elastic  fibers  are 
more  numerous  beneath  the  endothelium  on  the  inner  surface  of  the 
valves  (Ranvier,  89). 

if)  The  Capillaries. — The  capillaries  consist  solely  of  a  layer  of 
endothelial  cells,  accompanied  here  and  there  by  a  very  delicate  struc- 
tureless membrane,  and  rarely  by  stellate  connective-tissue  cells.  The 
connective  tissue  in  the  immediate  neighborhood  of  the  capillaries 
is  modified  to  such  an  extent  that  its  elements,  especially  those  of  a 
cellular  nature,  seem  to  be  arranged  in  a  direction  parallel  with  the 
long  axis  of  the  capillaries.      When  examined  in  suitable  prepara- 


THE    VASCULAR    SYSTEM. 


221 


tions,  the  endothelium  of  the  capillaries  is  seen  to  form  a  continuous 
layer,  the  cells  of  which  are,  as  a  rule,  greatly  flattened  and  present 
very  irregular  outlines. 

It  is  a  well-known  fact  that  a  migration  of  the  leucocytes  occurs 
from  the  capillaries  and  smaller  vessels  (compare  p.  193).  In  this 
connection  arises  the  question  as  to  whether  or  not  the  cells  pass 
through  certain  preformed  openings  in  the  endothelium  of  these 
vessels,  the  so-called  stomata,  or  through  the  stigmata  and  intercel- 
lular cement  uniting  the  endothelial  cells.  The  latter  seems  more 
probable,  as  stomata  do  not  occur  normally  in  the  capillary  wall. 
This  subject  will  be  further  touched  upon  in  the  description  of  the 
lymphatic  system. 

The  capillaries  connect  the  arterial  and  venous  precapillary  ves- 
sels, and  in  general  accommodate  themselves  to  the  shape  of  the 
elements  of  tissues  or  organs  in  which  they  are  situated.     In  the 


Fig.  176.— Endothelial  cells  of  capillary  (a)  and  precapillary  {ö)  from  the  mesentery  of 
rabbit :  stained  in  silver  nitrate. 


muscles  and  nerves,  etc.,  they  form  a  network  with  oblong  meshes, 
while  in  structures  having  a  considerable  surface,  such  as  the  pul- 
monary alveoli,  the  meshes  are  more  inclined  to  be  round  or  oval ; 
such  small  evaginations  of  tissue  as  the  papillae  of  the  skin  contain 
capillaries  arranged  in  the  shape  of  loops.  In  certain  organs — as,  for 
instance,  in  the  lobules  of  the  liver — the  capillaries  form  a  distinct 
network  with  small  meshes. 

Sinusoids. — In  connection  with  the  description  of  capillaries  we 
may  here  insert  a  brief  account  of  another  type  of  terminal  or 
peripheral  blood-channels,  described  by  Minot  under  the  name  of 
sinusoids;  his  account  is  here  followed.  The  sinusoids  are  also 
composed  only  of  endothelial  cells.  They  differ,  however,  from 
blood-capillaries  in  shape  and  size,  in  their  relation  to  the  cellular 
elements  of  the  tissues  in  which  they  are  found,  and  in  their  devel- 
opment. They  are  of  relatively  large  size,  and  vary  between  wide 
extremes.  They  are  of  very  irregular  shape  and  anastomose  freely. 
"A  sinusoid  has  its  eiKiothelium  closely  fitted  against  the  paren- 


222 


THE  CIRCULATORY  SYSTEM. 


chyma  of  the  organ,"  without  the  intervention  of  connective  tissue; 
or,  when  this  is  present,  usually  only  in  small  quantity,  it  is 
secondarily  acquired,  since  in  the  early  developmental  stages  of 
sinusoids  no  connective  tissue  intervenes  between  them  and  the 
parenchyma  of  the  tissue.  They  develop  by  the  intergrowth  and 
intercrescence  of  the  parenchyma  of  the  organ  and  venous  endothe- 
lium. Sinusoids  are  found  in  the  following  organs :  liver,  suprarenal, 
heart,  parathyroid,  carotid  gland,  spleen,  and  hemolymph  glands. 

(d)  Anastomoses,  Retia  mirabilia,  and  Sinuses. — In  the 
course  of  certain  vessels,  abrupt  changes  are  seen  to  occur — as,  for 
instance,  when  a  small  vessel  suddenly  breaks  up  into  a  network 
of  capillary  or  precapillary  vessels,  which,  after  continuing  as  such 
for  a  short  distance,  again  unite  to  form  a  larger  blood-channel, 
the  latter  then  dividing  as  usual  into  true  capillaries.  Such  struc- 
tures are  known  as  retia  mirabilia,  and  occur  in  man  in  the  kid- 

Sensory  nerve-ending. 

Plexus  of  vasomotor  nerves. 


Fig.    177. — Small  artery  from  the  oral  submucosa   of  cat,   stained  in   methylene- 
blue,  and  showing  a  small  portion  of  a  sensory  nerve-ending  and  the  plexus  of  vasomotor 


ney,  intestine,  etc.  Again,  instead  of  breaking  up  into  capillaries, 
a  vessel  may  empty  into  a  large  cavity  hned  by  endothelial  cells 
(blood  sinus).  The  latter  is  usually  surrounded  by  loose  con- 
nective tissue  and  is  capable  of  great  distention  when  filled  with 
blood  from  an  afferent  vessel,  or  when  the  lumen  of  the  efferent 
vessel  is  contracted  by  pressure  or  otherwise.  The  cavernous  or 
erectile  tissue  of  certain  organs  is  due  to  the  presence  of  such 
sinuses  (penis,  nasal  mucous  membrane,  etc.).  If  vessels  of  larger 
caliber  possess  numerous  direct  communications,  a  vascular  plexus 
is  the  result  ;  but  if  such  communications  occur  at  only  a  few 
points,  we  speak  of  anastomoses.  Especially  important  are  the 
direct  communications  between  arteries  and  veins  without  the 
mediation  of  capillaries.  Certain  structural  conditions  of  the  tis- 
sue appear  to  favor  such  anomalies,  which  occur  in  certain  exposed 


THE    LYMPHATIC    SYSTEM.  223 

areas  of  the  skin  (ear,  tip  of  nose,  toes)  and  in  the  meninges,  kid- 
ney, etc. 

The  blood-vessels,  and  more  particularly  the  arteries,  possess  a 
rich  nerve  supply,  comprising  both  nonmeduUated  and  medullated 
nerves.  The  nonmeduUated  nerves,  the  neuraxes  of  sympathetic 
neurones,  the  cell-bodies  of  which  are  situated  as  a  very  general 
rule  in  some  distant  ganglion,  form  plexuses  in  the  adventitia  of  the 
vessel-walls  ;  from  this,  single  nerve-fibers,  or  small  bundles  of  such, 
are  given  off,  which  enter  the  media  and,  after  repeated  division, 
end  on  the  involuntary  muscle-cells  in  a  manner  previously  de- 
scribed. (See  p.  166  and  Fig.  133.)  Through  the  agency  of  these 
nerves,  the  caliber  of  the  vessel  is  controlled.  They  are  known  as 
vasomotor  nerves.  Quite  recently  Dogiel,  Schemetkin,  and  Huber 
have  shown  that  many  vessels  possess  also  sensory  nerve-endings. 
The  medullated  nerve-fibers  terminating  in  such  endings,  branch 
repeatedly  before  losing  their  medullaiy  sheaths.  These  nerve-fibers 
with  their  branches  accompany  the  vessels  in  the  fibrous  tissue 
immediately  surrounding  the  adventitia.  The  nonmeduUated  ter- 
minal branches  end  in  telodendria,  consisting  of  small  fibrils,  beset 
with  large  varicosities  and  usually  terminating  in  relatively  large 
nodules. 

The  branches  and  telodendria  of  a  single  medullated  nerve-fiber 
(sensory  nerve)  terminating  in  a  vessel  are  often  spread  over  a 
relatively  large  area,  some  of  the  branches  of  such  a  nerve  often 
accompanying  an  arterial  branch,  to  terminate  thereon.  In  the 
large  vessels,  the  telodendria  of  the  sensory  nerves  are  found  not 
only  in  the  adventitia,  but  also  in  the  intima,  as  has  been  shown  by 
Schemetkin.     (See  p.  215.) 


B*  THE  LYMPHATIC  SYSTEM. 

U  LYMPH-VESSELS. 
The  larger  lymph-vessels — the  thoracic  duct,  the  lymphatic 
trunks,  and  the  lymph-vessels — have  relatively  thin  walls,  and 
their  structure  corresponds  in  general  to  that  of  the  veins.  They 
possess  numerous  valves,  and  are  subject  to  great  variation  in  cali- 
ber according  to  the  amount  of  their  contents.  When  empty,  they 
collapse  and  the  smaller  ones  are  not  easily  distinguished  from  the 
surrounding  connective  tissue.  Tiraofeew  and  Dogiel  (97)  have 
shown  that  the  lymph-vessels  are  supplied  with  nerves,  which  in 
their  arrangement  are  similar  to  those  found  in  the  arteries  and 
veins,  though  not  so  numerous.  The  latter,  who  has  given  the 
fuller  description,  states  that  the  nerves  supplying  the  lymph- 
vessels  are  varicose,  nonmeduUated  fibers  which  form  plexuses  sur- 
rounding these  structures.  The  terminal  branches  would  appear 
to  end  on  the  nonstriated  muscle  cells  found  in  the  wall  of  the 
lymph-vessel. 


224  THE    CIRCULATORY    SYSTEM, 

2.  LYMPH  CAPILLARIES,  LYMPH-SPACES,  AND  SEROUS  CAVITIES. 

The  walls  of  the  lymph  capillaries  consist  of  very  delicate,  flat- 
tened endothelial  cells,  which  are,  however,  somewhat  larger  and 
more  irregular  in  outline  than  those  of  the  vascular  capillaries.  The 
two  may  also  be  further  differentiated  by  the  fact  that  the  diameter 
of  the  lymph  capillaries  varies  greatly  within  very  short  distances. 
From  a  morphologic  standpoint,  the  relations  of  the  lymph  capil- 
laries to  the  vascular  capillaries  and  adjacent  tissues  are  among  the 
most  difficult  to  solve.  The  distribution  of  the  lymph-vessels  and 
capillaries  can  be  studied  only  in  injected  preparations,  and  it  is 
easily  seen  that  structures  of  such  elasticity  and  delicacy  are  pecu- 
liarly liable  to  injury  by  bursting  under  this  method  of  treatment. 
The  resulting  extravasations  of  the  injection-mass  then  spread  out 
in  the  direction  of  least  resistance  and  still  further  obscure  the 
picture,  rendering  it  difficult  to  determine  what  spaces  are  preformed 
and  what  are  the  result  of  the  injection.  So  much  is,  however,  cer- 
tain :  that  the  more  carefully  and  skilfully  the  injection  is  made,  the 
greater  are  the  areas  obtained,  showing  the  injection  of  true  lymph 
capillaries.  The  recent  work  of  W.  G.  MacCallum  confirms  this,  since 
he  has  shown  quite  conclusively  that  the  lymphatics  form  a  system  of 
channels,  with  continuous  walls,  and  are  thus  not  in  direct  commu- 
nication with  the  so-called  intercellular  lymph-spaces — the  lymph- 
canalicular  spaces.  Further  confirmation  of  the  fact  that  the 
lymphatics  form  a  closed  system  of  channels  is  found  in  the  excel- 
lent contribution  of  Dr.  Florence  R.  Sabin,  dealing  with  the 
development  of  the  lymphatic  system.  It  is  here  shown  that  the 
lymphatic  system  begins  as  two  blind  ducts,  guarded  by  valves, 
which  bud  off  from  the  veins  of  the  neck,  and  from  two  similar 
buds  which  arise  from  veins  in  the  inguinal  region.  These  buds 
grow  and  enlarge  to  form  lymph-hearts,  and  from  these  ducts  grow 
out  toward  the  skin,  which  they  invade  and  in  which  they  spread 
out  to  form  anastomosing  plexuses.  Ducts  also  grow  toward  the 
aorta  to  form  the  anlagen  for  the  thoracic  ducts,  and  from  these 
grow  out  and  invade  the  various  organs. 

In  some  regions  very  dense  networks  of  lymph  capillaries  sur- 
rounding the  smaller  blood-vessels  have  been  demonstrated.  Larger 
cleft-like  spaces,  lined  with  endothelium  and  communicating  with 
the  lymphatic  system,  are  also  found  surrounding  the  vessels,  peri- 
vascular spaces.  These  are  present  in  man  in  the  Haversian  canals 
of  bone  tissue,  around  the  vessels  of  the  central  nervous  system, 
etc.,  and  are  separated  from  the  actual  vessel-wall  by  flattened  endo- 
thelial cells.  As  in  the  case  of  the  so-called  perilympliatic  spaces, 
the  walls  of  the  perivascular  spaces  are  joined  here  and  there  by 
connective-tissue  trabeculae  covered  by  endothelium.  Such  struc- 
tures exist  in  the  perilymphatic  spaces  of  the  ear,  the  subdural 
spaces  of  the  pia,  the  subarachnoidal  space,  the  lymph-sinuses,  etc. 
The  perivascular  spaces  are  better  developed  in  the  lower  animals 
(amphibia,  reptilia,  etc.)  than  in  mammalia. 


THE    CAROTID    GLAND, 


225 


Mention  has  been  made  of  the  migration  of  leucocytes  and, 
under  certain  conditions,  of  red  blood-cells  through  the  walls  of 
blood  capillaries,  and  in  the  case  of  the  former  through  the  walls  of 
lymph  capillaries  and  lymph-vessels  and  spaces.  This  diapedesis  of 
leucocytes  probably  takes  place  by  a  wandering  of  these  cells 
through  the  intercellular  cement  uniting  the  endothelial  cells  lining 
these  spaces.  According  to  later  investigations,  it  would  seem  that 
leucocytes  may  bore  through  endothelial  cells,  and  thus  migrate 
from  the  vessel  or  space  in  which  they  are  found  previous  to  such 
migration. 


C  THE  CAROTID  GLAND    (GLANDULA  CAROTICA, 
GLOMUS  CAROTICUM). 

At  the  point  where  the  common  carotid  divides,  there  lies  in 
man  a  small  oval  structure  about  the  size  of  a  grain  of  wheat,  known 
as  the  carotid  gland  or  the  glomus  caroticum.      It  is  imbedded  in 


Septum. 


Trabecula  of 
cells  in  cross- 
section. 

Distended 
blood  capil- 
laries. 


=ri.  Efferent  vein. 


Fig.  178. — Section  of  a  cell-ball  from  the  glomus  caroticum  of  man  ;   X  l^O-     (Injected 
specimen,  after  Schaper.) 


connective  tissue,  surrounded  by  many  nerve-fibers,  and  on  account 
of  its  great  vascularity  has  a  decidedly  red  color.  The  connective- 
tissue  envelope  of  the  gland  penetrates  into  the  interior  in  the  form 
of  septa,  which  divide  its  substance  into  small  lobules,  and  these  in 
turn  into  smaller  round  masses,  the  cell-balls.  A  small  branch 
from  the  internal  or  external  carotid  enters  the  gland,  where 
it  branches,  sending  off  twigs  to  the  lobules,  and  these  in  turn  still 
15 


226  THE  CIRCULATORY  SYSTEM. 

smaller  divisions  to  the  cell-balls.  The  latter  vessels  break  up  into 
capillaries,  which  merge  at  the  periphery  of  each  cell-ball  to  form  a 
small  vein,  from  which  the  larger  trunks  that  pass  from  the  lobules 
are  derived.  Each  lobule  is  thus  surrounded  by  a  venous  plexus 
from  which  the  larger  veins  originate  that  leave  the  organ  at  sev- 
eral points.  The  cell-balls  are  composed  of  cellular  cords,  or 
trabeculse,  the  elements  of  which  are  extremely  sensitive  to  the 
action  of  reagents.  The  cells  are  round  or  irregularly  polygonal 
and  separated  from  each  other  by  a  scanty  reticular  connective 
tissue.  The  capillaries  already  mentioned  come  in  direct  contact 
with  the  cells  of  the  cell-balls.  The  organ  contains  a  relatively 
large  number  of  nerve-fibers  and  a  few  ganglion  cells. 

As  the  individual  grows  older,  the  organ  undergoes  changes 
which  finally  make  it  unrecognizable.  The  former  belief  that  the 
carotid  gland  was  developed  as  an  evagination  of  one  of  the  visceral 
pouches  has  been  replaced  by  a  newer  theory  which  gives  it  an 
origin  solely  from  the  vessel-wall  {vid.  Schaper).  The  structure  of 
the  coccygeal  gland  is  in  general  like  that  of  the  carotid  gland 
here  described. 

TECHNIG  (BLOOD  AND  BLOOD-FORMING  ORGANS). 

Red  blood-corpuscles  may  be  examined  in  the  blood  fluid  without 
special  preparation.  The  tip  of  the  finger  is  punctured  and  a  small  drop 
of  blood  pressed  out,  placed  upon  a  slide,  and  immediately  covered 
with  a  cover-glass  and  examined.  In  such  preparations  the  red  blood- 
cells  soon  become  crenated.  The  evaporation  causing  the  crenation  may 
be  prevented  by  surrounding  the  cover-glass  with  oil  (olive  oil).  A  fluid 
having  but  slight  effect  upon  the  red  blood-cells  is  Hayem's  solution, 
which,  however,  is  not  adapted  to  the  examination  of  leucocytes.  It 
consists  of  sodium  chlorid  i  gm.,  sulphate  of  soda  5  gm.,  corrosive  subli- 
mate 0.5  gm.,  and  water  200  gm.  The  fresh  blood  is  brought  directly 
into  this  solution,  the  amount  of  which  should  be  at  least  one  hundred 
times  the  volume  of  the  blood  to  be  examined.  The  fixed  blood-cells 
sink  to  the  bottom,  and  after  twenty-four  hours  the  fluid  is  carefully 
poured  off  and  replaced  by  water.  The  blood-corpuscles  are  then 
removed  with  a  pipet  and  examined  in  dilute  glycerin.  They  may  be 
stained  with  eosin  and  hematoxylin. 

Fresh  red  blood-corpuscles  may  also  be  fixed  in  osmic  acid  and 
other  special  fixing  agents.  This  is  done  by  dropping  a  small  quantity  of 
blood  into  the  fixing  fluid  ;  the  blood-cells  immediately  sink  and  allow 
the  osmic  acid  to  be  decanted  ;  they  are  then  washed  with  water,  drawn 
up  with  a  pipet,  and  examined  in  dilute  glycerin. 

Cover=gIass  Preparations. — A  method  almost  universally  used  con- 
sists in  preserving  the  blood-corpuscles  in  dry  preparations.  A  drop  of 
fresh  blood  is  placed  between  two  thoroughly  cleaned  cover -glasses,  which 
are  then  quickly  drawn  apart,  leaving  on  the  surface  of  each  a  thin  film  of 
blood  which  dries  in  a  few  moments  at  ordinary  room  temperature.  The 
specimens  are  further  dried  for  several  hours  at  a  temperature  of  120°  C. 
After  they  have  been  subjected  to  this  process,  they  may  be  stained,  etc. 
The  same  results  may  be  obtained  by  treating  specimens  dried  in  the  air 


TECHNIC    (blood    AND    BLOOD-FORMING    ORGANS).  22/ 

with  a  solution  of  equal  parts  of  alcohol  and  ether  for  from  one  to  twenty- 
four  hours,  after  which  they  are  again  dried  in  the  air,  and  are  then  ready 
for  further  treatment. 

A  cover-glass  preparation  of  fresh  blood  may  also  be  treated  for  a 
quarter  of  an  hour  with  a  concentrated  solution  of  corrosive  sublimate  in 
saline  solution,  then  washed  with  water,  stained,  dehydrated  with  alcohol 
and  mounted  in  Canada  balsam.  A  concentrated  aqueous  solution  of 
picric  acid  may  also  be  used,  but  in  this  case  the  specimen  should  remain 
in  it  for  from  twelve  to  twenty-four  hours. 

The  elements  of  the  blood  may  also  be  examined  in  sections. 
Small  vessels  are  ligated  at  both  ends,  removed,  fixed  with  osmic  acid, 
corrosive  sublimate,  or  picric  acid,  and  imbedded  in  paraffin. 

After  fixation  by  any  of  the  above  methods  the  blood-cells  may 
be  stained.  Eosin  brings  out  very  well  the  hemoglobin  in  the  blood- 
cells,  coloring  it  a  brilliant  red ;  the  stain  should  be  used  in  very  dilute 
aqueous  or  alcoholic  solutions  (i^  or  less),  or  in  combination  w-ith  alum 
(eosin  i  gm.,  alum  i  gm.,  and  absolute  alcohol  200  c.c,  E.  Fischer). 
Eosin  may  also  be  used  as  a  counterstain  subsequent  to  a  nuclear  stain — 
for  instance,  hematoxylin.  The  preparation  is  stained  for  about  ten  min- 
utes, then  washed  in  water  or  placed  in  alcohol  until  the  blood-cells  alone 
remain  colored ;  the  cover-glass  preparation  should  then  be  thoroughly 
dried  between  filter-paper  and  mounted  in  Canada  balsam.  Besides 
eosin,  other  acid  stains — as  orange  G,  indulin,  and  nigrosin — have  the 
property  of  coloring  blood-cells  containing  hemoglobin. 

Blood  platelets  are  best  fixed  with  osmic  acid,  and  may  be  seen 
without  staining.  They  may  also  be  stained  and  preserved  in  a  sodium 
chlorid  solution  to  w^hich  methyl -violet  is  added  in  a  proportion  of 
I  :  20000  (Bizzozero,  82).  Afanassiew  adds  0.6^  of  dry  peptone  to 
the  solution  (this  fluid  must  be  sterilized  before  using). 

Ehrlich's  Granulations. — The  leucocytes  of  the  circulating  blood 
and  those  found  in  certain  organs  possess  granulations  which  werp  first 
studied  by  Ehrlich  and  his  pupils,  and  which  may  be  demonstrated  by 
certain  methods.  The  names  given  to  these  granulations  are  based  upon 
Ehrlich's  classification  of  the  anilin  stains,  which  differs  from  that  of  the 
chemist.  This  author  distinguishes  acid,  basic,  and  neutral  stains.  By 
the  acid  stains  he  understands  those  combinations  in  which  the  acid  is  the 
active  staining  principle,  as  in  the  case  of  the  picrate  of  ammonia. 
Among  these  are  congo,  eosin,  orange  G,  indulin,  and  nigrosin.  The 
basic  stains  are  those  which,  like  the  acetate  of  rosanilin,  consist  of  a 
color  base  and  an  indifferent  acid.  To  these  belong  fuchsin,  Bismarck 
brown,  safranin,  gentian,  dahlia,  methyl-violet,  methylene-blue,  and  tolui- 
din.  Finally,  the  neutral  anilins  may  be  considered  as  those  stains  which, 
like  the  picrate  of  rosanilin,  are  formed  by  the  union  of  a  color  base  with 
a  color  acid.  The  granula  may  be  demonstrated  in  dry  preparations  as 
well  as  in  those  fixed  with  alcohol,  corrosive  sublimate,  glacial  acetic  acid, 
and  sometimes  even  Flemming's  solution.  Five  kinds  of  granules  are 
distinguished,  and  designated  by  the  Greek  letters  from  alpha  to  epsilon. 
The  «-granules  (acidophile,  eosinophile)  occur  in  leucocytes 
of  the  normal  blood,  in  the  lymph,  and  in  the  tissues,  and  are  differen- 
tiated from  the  others  by  their  peculiar  staining  reaction  to  all  acid  stains. 
They  are  first  treated  for  some  hours  with  a  saturated  solution  of  an  acid 


228  THE    CIRCULATORY    SYSTEM. 

Stain  f  preferably  eosin)  in  glycerin,  washed  with  water,  subsequently  col- 
ored with  a  nuclear  stain  (as  hematoxylin  or  methylene-blue),  and  then 
dried  and  mounted  in  Canada  balsam.  Sections  may  be  treated  in  the 
same  way,  with  the  exception  that  after  being  washed  with  water,  they 
are  first  dehydrated  with  absolute  alcohol  before  mounting  in  balsam. 

Another  method  by  which  both  nuclei  and  granules  are  stained 
consists  in  the  use  of  Ehrlich's  hematoxylin  solution  (see  page  43), 
to  which  0.5'^  eosin  is  added.  Before  using,  the  solution  should 
be  permitted  to  stand  exposed  to  the  light  for  three  weeks.  This  mixture 
stains  in  a  few  hours,  after  which  the  preparation  is  washed  with  water, 
treated  with  alcohol,  and  then  mounted  in  Canada  balsam.  The 
a-granules  appear  red,  the  nuclei  blue. 

The  /3-granules  (amphophile,  indulinophile)  stain  as  well  in 
acid  as  in  basic  anilins.  They  do  not  occur  in  man,  but  may  be  observed 
in  the  blood  of  guinea-pigs,  fowl,  rabbits,  etc.  They  are  demonstrated 
as  follows  :  Equal  parts  of  saturated  glycerin  solutions  of  eosin,  naph- 
thylamin-yellow,  and  indulin  are  mixed,  and  the  dried  preparations  treated 
with  this  combination  for  a  few  hours,  then  washed  with  water,  dried 
between  filter-paper,  and  mounted  in  Canada  balsam.  The  amphophile 
granules  are  stained  black,  the  eosinophile  granules  red,  the  nuclei  black, 
and  the  hemoglobin  yellow. 

The  ^-granules,  or  those  of  the  mast=cells,  are  found  in  normal 
tissues  and  also  in  small  quantities  in  normal  blood,  and  are  found  in 
larger  numbers  in  leukemic  blood.  They  may  be  shown  by  two  methods  : 
( I )  A  mixture  is  made  consisting  of  concentrated  solution  of  dahlia  in 
glacial  acetic  acid  12.5  c.c,  absolute  alcohol  50  c.c. ,  distilled  water  100 
c.c.  (Ehrlich).  The  treatment  is  the  same  as  for  the  amphophile  gran- 
ules ;  (2)  Westphal's  alum-carmin-dahlia  solution  (57/0^.  Ehrlich).  This 
mixture  is  used  in  staining  dry  preparations  as  well  as  sections  of  objects 
fixed  for  at  least  one  week  in  alcohol.  Alum  i  gm.  is  dissolved  in  dis- 
tilled water  100  c.c,  and  carmin  i  gm.  added.  The  whole  is  then 
boiled  for  one-quarter  hour,  cooled,  filtered,  and  0.5  c.c.  of  carbolic 
acid  added  (Grenacher's  alum-carmin,  see  page  42).  This  solution  is 
now  mixed  with  100  c.c.  of  a  saturated  solution  of  dahlia  in  absolute 
alcohol,  glycerin  50  c.c,  and  glacial  acetic  acid  10  c.c,  the  whole  stirred 
and  allowed  to  stand  for  a  time.  The  specimen  is  stained  for  twenty-four 
hours,  decolorized  in  absolute  alcohol  for  the  same  length  of  time,  and 
finally  mounted  in  Canada  balsam.  The  j'-granules  are  colored  a  dark 
blue  and  the  nuclei  red.  A  simpler  method  of  demonstrating  the 
^'-granules  consists  in  overstaining  dry  and  fixed  cover-glass  preparations 
with  a  saturated  aqueous  solution  of  methylene-blue,  decolorizing  for  some 
time  in  absolute  alcohol,  drying  between  filter-papers,  and  mounting  in 
Canada  balsam. 

The  ^-granules  (basophile)  occur  in  mononuclear  leucocytes 
of  the  human  blood.  Their  staining  may  be  accomplished  in  a  few  min- 
utes by  treating  fixed  cover-glass  preparations  with  a  concentrated  aqueous 
solution  of  methylene-blue,  after  which  they  are  washed  with  water,  dried 
between  filter-papers,  and  mounted  in  Canada  balsam. 

The  e-  or  neutrophile  granules  which  are  found  normally  in 
the  polynuclear  leucocytes  of  man  (as  also  in  pus-cells),  in  some  of  the 
transitional  cells,  and  in  the  myelocytes,  are  stained  by  Ehrlich  as  follows  : 
5  vols,  of  a  saturated  aqueous  solution  of  acid  fuchsin  are  mixed  with  i  vol. 


TECHNIC    (blood    AND    BLOOD-FORMING    ORGANS).  229 

of  a  concentrated  aqueous  solution  of  methylene-blue.  To  this  5  vols,  of 
water  are  added,  and  the  whole  allowed  to  stand  for  a  few  days,  after 
which  the  solution  is  filtered.  This  mixture  stains  in  five  minutes,  and 
the  specimen  is  then  washed  with  water,  etc.  The  neutrophile  granules 
are  colored  green,  the  eosinophile  granules  red  and  the  hemoglobin 
yellow. 

Neutrophile  and  eosinophile  granules  may  also  be  stained  in 
Ehrlich' s  neutrophile  mixture  : 

Orange  G,  saturated  aqueous  solution,     .    .  1 30  to  135  c.c. 
Acid  fuchsin,    "  "  "  .    .    80  to  120  " 

Methyl-green,  "  "  "  .    .  125  " 

Distilled  water, 300  " 

Absolute  alcohol, 200  " 

Glycerin, loo  " 

Mix  the  above  quantities  of  orange  G,  acid  fuchsin,  water,  and  alco- 
hol in  a  bottle  and  add  slowly,  while  shaking  the  bottle,  the  methyl -green 
and  finally  the  glycerin.  The  cover-glass  preparations  should  be  fixed  in 
the  ether  and  alcohol  solution  for  about  one  hour,  or  fixed  with  dry  heat 
at  a  temperature  of  110°  C.  for  from  fifteen  to  thirty  minutes.  Float 
the  preparation  on  a  small  quantity  of  the  stain  for  about  fifteen  minutes, 
wash  in  water,  dry  and  mount  in  balsam.  The  red  blood-cells  are  stained 
a  reddish -brown  color  (brick-color),  all  nuclei  a  light  blue-gieen,  the 
eosinophile  granules  a  fuchsin-red,  and  the  neutrophile  granules  a  violet- 
red.  Grübler,  of  Leipzig,  has  prepared  a  dry  powder,  known  as  the 
Ehrlich-Biondi-Heidenhain  three-color  mixture,  which  is  prepared  for 
use  by  making  a  0.4^  solution  in  distilled  water,  to  100  c.c.  of  which 
are  added  7  c.c.  of  a  0.5%  aqueous  solution  of  acid  fuchsin. 

Wright's  Method  of  Staining  Blood  Films. — This  excellent  and 
rapid  method  is  especially  recommended. 

Stain. — Make  a  one-half  per  cent,  aqueous  solution  of  sodium  bicar- 
bonate in  an  Erlenmeyer  flask  and  add  to  it  one  per  cent,  of  methylene- 
blue.  Steam  for  one  hour  in  an  Arnold  steam  sterilizer  and  allow 
mixture  to  cool,  and  when  it  is  cold  pour  in  a  large  dish.  To  100  c.c. 
of  this  solution  add  about  500  c.c.  of  a  one-tenth  per  cent,  aqueous 
solution  of  eosin  ( Grübler' s  yellowish  eosin,  soluble  in  water).  The 
quantity  of  the  eosin  solution  can  not  be  definitely  given ;  it  is  added 
while  constantly  stirring  until  the  solution  becomes  of  purple  color  and 
a  yellowish  scum  with  metallic  luster  forms  on  the  surface  and  a  finely 
granular  black  precipitate  appears  in  suspension.  The  precipitate  is  col- 
lected on  a  filter  and  allowed  to  dry  thoroughly.  Make  a  saturated  solu- 
tion in  pure  methylic  alcohol  (0.3  gm.  of  precipitate  to  100  c.c.  of 
methylic  alcohol)  and  filter.  To  80  c.c.  of  the  filtrate  20  c.c.  of  meth- 
ylic alcohol  is  added  to  complete  the  stain. 

Staining  of  Blood  Films. — Allow  blood  film  to  dry  in  the  air  and 
pour  as  much  of  the  stain  on  the  cover-glass  or  slide  as  it  will  hold, 
allowing  it  to  remain  in  contact  with  the  preparation  for  about  one 
minute  ;  then  add,  drop  by  drop,  enough  water  to  make  the  stain  semi- 
transparent,  and  a  reddish  tinge  appears  at  the  borders  and  a  metallic 
scum  on  the  surface.  This  diluted  stain  remains  on  the  preparation  two 
or  three  minutes.  The  preparation  is  now  washed  in  distilled  water 
until  the  better  parts  have  a  yellowish  or  reddish  color.  Dry  quickly 
between  filter-papers  and  mount  on  balsam.      Red  cells  are  orange  or 


230  THE    CIRCULATORY    SYSTEM. 

pink  in  color ;  the  nuclei,  of  blue  color  of  varying  intensity,  eosinophile 
granules  red,  neutrophile  granules  reddish-lilac,  basophile  granules  dark 
blue  or  almost  black. 

The  hemoglobin  shows  itself  in  the  form  of  crystals.  In  certain 
teleosts  the  crystals  are  formed  in  the  blood-corpuscles  around  the  nuclei 
and  often  within  a  short  time  after  death.  In  old  alcoholic  specimens, 
hemoglobin  crystals  (blood  crystals)  are  found  in  the  vessels  and  were 
first  discovered  here  by  Reichert  in  the  blood  of  the  guinea-pig.  They 
have  been  found  in  large  quantities  in  the  splenic  blood  of  a  sturgeon 
which  had  been  preserved  for  forty  years  in  alcohol.  The  hemoglobin 
crystals  belong  to  the  rhombic  series  of  crystallographic  classification. 
The  simplest  method  of  demonstrating  hemoglobin  crystals  is  probably 
the  following  :  The  blood  is  first  defibrinated  by  whipping  or  agitating 
with  mercury,  after  which  process  sulphuric  ether  is  added,  drop  by  drop, 
until  the  mixture  has  been  made  laky ;  this  change  may  be  detected 
macroscopically  by  the  sudden  change  from  an  opaque  to  a  dark,  trans- 
parent, cherry-red  color.  No  red  blood-cells  should  now  be  seen  under 
the  microscope.  The  preparation  is  placed  on  ice  for  from  twelve  to 
twenty-four  hours  after  which  a  drop  of  the  blood  is  placed  on  a  slide. 
In  half  an  hour  it  will  be  seen  that  the  margin  of  the  drop  has  begun  to 
dry.  A  cover-slip  is  now  applied  and,  after  a  few  minutes,  numerous 
crystals  are  seen  to  form  at  the  margin  of  the  drop,  a  process  which  may 
be  followed  under  the  microscope.  Large  hemoglobin  crystals  are  ob- 
tained by  Gscheidtlen  as  follows :  Defibrinated  blood  is  placed  in  a 
glass  tube,  which  is  then  hermetically  sealed.  The  blood  is  now  sub- 
jected to  a  temperature  of  about  40°  C.  for  two  or  three  days  ;  if 
then  the  glass  be  broken  and  the  blood  poured  into  a  flat  dish,  large 
hemoglobin  crystals  are  immediately  formed.  Crystals  also  appear  if  a 
drop  of  laky  blood  be  placed  in  a  thick  solution  of  Canada  balsam  in 
chloroform  and  covered  with  a  cover-slip. 

Hemin  crystals  (Teichmann's  crystals  ;  hemin  is  hematin-chlorid) 
in  the  shape  of  rhombic  plates  are  very  easily' obtained  from  the  blood. 
A  drop  of  the  latter  is  placed  on  a  slide  and  carefully  mixed  with  a  small 
drop  of  normal  salt  solution.  This  is  then  carefully  warmed  until  the 
fluid  evaporates  and  leaves  a  reddish-brown  residue,  after  which  a  cover- 
glass  is  applied  and  glacial  acetic  acid  added  until  the  space  between 
slide  and  cover-glass  is  filled.  The  preparation  is  now  heated  until  the 
acetic  acid  boils.  As  soon  as  the  latter  evaporates,  Canada  balsam  may 
be  brought  under  the  cover-glass,  thus  producing  a  permanent  specimen. 
When  fluids  or  stains  suspected  of  containing  blood  are  to  be  examined, 
the  hemin  crystals  become  of  the  utmost  importance,  as  their  demonstra- 
tion is  then  a  positive  indication  of  the  presence  of  blood.  Fluids  are 
evaporated  and  treated  with  glacial  acetic  acid  as  above  directed.  Sus- 
pected blood  stains  on  cloth  are  treated  as  follows :  Small  pieces  are  cut 
from  the  cloth  in  the  region  of  the  stain,  soaked  in  normal  salt  solution, 
and  the  resulting  fluid  treated  as  above.  If  the  stain  is  on  wood  or  other 
solid  object,  the  stain  is  scraped  off  and  dissolved  in  normal  salt  and 
then  tested  for  hemin  crystals.  Hemin  crystals  are  almost  or  entirely 
insoluble  in  water,  alcohol,  ether,  ammonia,  glacial  acetic  acid,  dilute 
sulphuric  acid,  and  nitric  acid.  They  are,  however,  soluble  in  potassium 
hydrate. 

A  third  form  of  crystals  occasionally  found  in  the  blood  and  fre- 
quently in  the  corpora  lutea  and,  under  pathologic  conditions,  also  in  apo- 


TECHNIC    (blood    AND    BLOOD-FORMING    ORGANS).  23 1 

plectic  areas,  are  the  hematoidin  crystals  first  discovered  by  Virchow. 
Masses  of  these  crystals  have  an  orange  color.  Microscopically,  they 
appear  as  red  rhombic  plates.  As  they  are  soluble  in  neither  alcohol 
nor  chloroform,  they  are  easily  preserved  in  Canada  balsam.  Their 
artificial  production  has  as  yet  never  been  accomplished.  Hematoidin 
contains  no  iron. 

The  fibrin  thrown  down  when  the  blood  coagulates  may  be  dem- 
onstrated upon  the  slide  in  the  form  of  very  fine  particles  and  fila- 
ments. A  drop  of  blood  is  brought  upon  the  slide  and  kept  for  a  time  in 
a  moist  chamber  or  on  the  table  until  it  begins  to  clot ;  after  which  a 
cover-slip  is  applied  and  the  preparation  washed  with  water  by  continued 
irrigation.  In  this  manner  most  of  the  red  blood-corpuscles  are  removed. 
Lugol  solution  may  now  be  added,  which  stains  brown  the  filaments  of 
the  fibrin  network  adherent  to  the  slide.  '  In  order  to  see  the  fibrin  net- 
work in  sections,  it  is  better  to  use  specimens  previously  fixed  in  alcohol ; 
the  sections  are  stained  for  ten  minutes  in  a  concentrated  solution  of  gen- 
tian-violet in  anilin  water  (Weigert),  rinsed  in  normal  salt  solution, 
treated  for  about  ten  minutes  with  iodo-iodid  of  potassium  solution,  and 
then  spread  upon  a  slide  and  dried  with  filter-paper.  They  are  now 
placed  in  a  solution  consisting  of  2  parts  of  anilin  oil  and  i  part  of  xylol 
until  they  become  perfectly  transparent.  This  solution  is  then  replaced 
by  pure  xylol  and  finally  by  Canada  balsam.  The  fibrin  network  is 
stained  a  deep  violet. 

Blood  Current. — There  are  different  methods  and  a  variety  of  mate- 
rial at  our  disposal  for  the  demonstration  of  the  blood  current  through  the' 
vessels.  The  best  object  for  this  purpose  is  probably  the  frog.  The  proce- 
dure is  as  follows :  The  animal  is  immobilized  by  poisoning  with  curare.  ^ 
gm.  of  a  I  %  aqueous  solution  injected  into  the  dorsal  lymph-sac  will  immo- 
bilize the  frog  in  a  short  time.  The  exact  dose  can  not,  however,  be  given, 
as  the  commercial  curare  is  not  a  uniform  chemical  compound  ;  the  dose 
must  therefore  be  ascertained  by  experiment.  As  is  well  known,  curare 
affects  exclusively  the  nerve  end-organs  of  striated  voluntary  muscle,  but 
does  not  affect  either  the  heart  muscle  or  unstriated  muscular  tissue  ;  hence 
the  utility  of  curare  for  this  purpose.  In  order  to  see  the  blood  current, 
it  is  only  necessary  to  stretch  the  transparent  web  between  the  frog's  toes 
and  fasten  it  with  insect  needles  to  a  cork  plate  having  a  suitable  open- 
ing. If  the  cork  plate  be  large  enough  to  accommodate  the  whole  frog, 
it  may  be  placed  in  such  a  position  that  its  opening  lies  over  that  in  the 
stage  of  the  microscope.  The  web  thus  spread  out  may  be  examined 
with  a  medium  magnification.  The  tongue  of  the  frog  is  also  used  for  the 
same  purpose.  As  the  latter  is  attached  to  the  anterior  angle  of  the  lower 
jaw,  it  may  be  conveniently  drawn  out,  suitably  stretched,  and  then 
placed  over  the  hole  in  the  cork  plate.  A  very  good  view  of  the  circula- 
tion may  be  obtained  by  examining  the  mesentery  of  a  frog.  The  migra- 
tion of  the  leucocytes  through  the  vessel -walls  can  also  be  studied  in  such 
preparations.  An  incision  0.5  cm.  in  length  is  made  in  the  right  axillary 
line  through  the  skin  of  a  frog  (best  in  the  male),  care  being  taken  not  to 
injure  any  vessels  (which  can  be  seen  through  the  skin  in  frogs  possessing 
little  pigment).  The  abdominal  muscles  are  then  incised  and  a  pair  of  ■ 
forceps  introduced  to  grasp  one  of  the  presenting  intestinal  loops.  The 
latter  is  then  attached  to  the  cork  plate  with  needles,  and  the  mesentery 
carefully  stretched  over  the  opening.  On  examining  the  specimen  it  is 
best  to  moisten  it  with  normal  salt  solution  and  to  cover  the  area  to  be 


232 


THE    CIRCULATORY    SYSTEM. 


examined  with  a  fragment  of  a  cover-glass.     The  lung  may  also  be  ex- 
amined, but  here  the  incision  must  be  farther  forward. 

Counting  BIood=cells. — The  instrument  now  generally  used  for  this 
purpose  is  the  Thoma-Zeiss  hemocytometer.  This  apparatus  consists  of 
two  parts  :  pipettes  by  means  of  which  the  blood  is  diluted  loo  times, 
when  counting  red,  or  lo  times  when  white  blood-cells  are  to  be  counted, 
and  a  glass  slide,  on  which  there  is  a  small  well  of  known  depth,  the  bot- 
tom of  the  well  being  divided  off  into  small  squares.  The  pipette  used  when 
counting  the  red  cells  consists  of  a  capillary  tube,  near  the  middle  of 
which  there  is  an  ampullar  enlargement.  This  is  so  graduated  that  the 
cubical  contents  of  the  capillary  tube  is  just  one-hundredth  part  of  the 
cubical  contents  of  the  ampulla.  The  blood  to  be  examined  is  drawn 
into  the  capillary  tube  to  a  line  marked  i  (just  below  the  ampulla) ;  the 
end  of  the  pipette  is  then  inserted  into  the  diluting  fluid,  and  this  is 
sucked  up  until  the  diluted  blood  reaches  a  line  marked  loi  (just  above 


Fig.  179. — Thoma-Zeiss  hemocytometer:  a,  Slide  used  in  counting ;   b,  sectional  view ; 
c,  a  portion  of  ruled  bottom  of  the  well  ;  d,  pipette. 


the  ampulla).     The  pipette  is  then  carefully  shaken  to  mix  thoroughly 
the  blood  and  the  diluting  fluid. 

Either  of  the  following  two  solutions  may  be  used  for  diluting  the 
blood : 

Hayem' s  Solution  : 

Bichlorid  of  mercury 0.5  gm. 

Sodium  chlorid i  .0  gm. 

Sodium  sulphate 5.0  gm. 

Distilled  water 2co.o  c.c. 

Toison' s  Fluid  (^as  given  by  V.  Kahlden~)  : 

Methyl  violet  5  B 0.025  g™- 

Neutral  glycerin 30.0  c.c. 

Distilled  water 80.0  c.c. 

Mix  the  methyl  violet  with  the  glycerin  and  distilled  water  ;  to  this 
solution  is  added — 

Sodium  chlorid  (C.  P.)       I.o  gm. 

Sodium  sulphate  (C.  P.) 8.0  gm. 

Distilled  water 80.0  c.c. 


TECHNIC    (blood    AND    BLOOD-FORMING    ORGANS).  233 

Filter,  and  the  solution  will  be  ready  for  use.  The  white  blood-cells 
are  stained  violet,  and  may  thus  be  counted  with  the  red. 

The  diluting  fluid  contained  in  the  capillary  tube  is  then  blown  out, 
and  a  small  drop  of  the  diluted  blood  is  placed  on  the  center  of  the  small 
glass  disc.  The  small  disc  is  surrounded  by  a  ring  of  glass,  cemented  to 
the  slide.  This  glass  ring  is  o.i  mm.  thicker  than  the  glass  disc.  When 
this  small  chamber  is  covered  with  a  thick  cover-glass,  we  have  a  layer 
of  blood  0.1  mm.  deep  between  the  disc  and  the  cover-glass.  On  the 
upper  surface  of  the  small  glass  disc  (on  which  the  drop  of  diluted  blood 
was  placed)  there  are  marked  off  400  small  squares.  The  sides  of  the 
small  squares  are  ^\  mm.  long.  It  will  be  seen  that  the  layer  of  blood 
over  each  of  the  squares  would  have  a  cubical  contents  of— 

^öVö  of  ^  cubic  millimeter  {^\  X  2V  X  to  =  ?öVö)  • 

The  hemocytometer  slide  is  now  placed  on  the  stage  of  the  micro- 
scope, where  it  should  remain  undisturbed  for  several  minutes  before 
counting.  The  red  blood-cells  in  25  to  50  squares  are  then  counted. 
To  ascertain  the  number  of  red  cells  in  a  cubic  millimeter  the  following 
formula  may  be  useful : 

reach    mass    of^  [dilution,!    ^„   fredcellsl         \ 

4000     blood  counted,       X^  |  here  icoj  X"  |  counted  |  ^^„^^er  of  red 


n  (number  of  squares  counted) 


blood-cells 


[ 


Or,  ascertain  the  average  of  the  red  blood-cells  in  the  squares 
counted,  and  multiply  this  number  by  400,000. 

In  case  it  is  desired  to  count  only  the  white  blood-corpuscles,  a  i^  per 
cent,  solution  of  glacial  acetic  acid  is  used  for  diluting  the  blood.  This 
solution  bleaches  the  red  cells,  and  brings  out  clearly  the  white  corpuscles. 

The  blood  is  diluted  only  ten  times,  using  for  this  purpose  the  Thoma- 
Zeiss  pipette  for  counting  white  corpuscles.  The  formula  then  reads  as 
follows  : 

(the  number  of  white "| 
blood-corpuscles  V  ,         r     t,-. 

counted.  J        the  number  of  white 

. =:  blood-cells  found  m 

n  (number  of  squares  counted).  a  cubic  millimeter. 

Or,  multiply  the  average  number  of  white  corpuscles  in  each  square 
by  40,000. 

Lymph=glands. — To  obtain  a  general  idea  of  the  structure  of 
lymphatic  glands,  sections  are  made  of  small  glands  fixed  in  alcohol  or 
corrosive  sublimate.  They  are  then  stained  with  hematoxylin  and  eosin. 
In  such  preparations  the  cortical  and  medullary  substances  can  be  studied  ; 
the  trabeculae  and  blood  take  the  eosin  stain. 

The  flattened  endothelial  cells  covering  the  trabeculae  are  brought 
to  view  by  injecting  a  o.ifo  solution  of  silver  nitrate  into  a  fresh  lymph- 
atic gland.  After  half  an  hour  the  gland  is  fixed  with  alcohol  and  car- 
ried through  in  the  regular  way  ;  the  sections  should  be  quite  thick  (not 
under  20  m).  After  the  sections  have  been  mounted  in  Canada  balsam 
and  exposed  to  light  for  a  short  time,  the  endothelial  mosaic  will  be  seen 
wherever  the  silver  nitrate  has  penetrated. 


234  THE    CIRCULATORY    SYSTEM. 

Fixing  with  Flemming's  solution  and  staining  with  safranin  is 
the  best  method  for  studying  the  germ  centers  of  the  lymph-follicles. 
Other  fluids  which  bring  out  the  mitoses  may  also  be  employed. 

Reticular  tissue  is  best  demonstrated  by  sectioning  a  fresh  gland 
with  a  freezing  microtome,  removing  a  section  to  a  test-tube  one-quarter 
filled  with  water,  and  agitating  it.  The  lymphocytes  are  thus  shaken  out 
of  the  meshes  of  the  reticulum,  leaving  the  latter  free  for  examination. 

The  same  results  can  be  obtained  by  placing  a  section  prepared 
in  the  above-named  manner  upon  a  slide,  wetting  it  with  water,  and 
carefully  going  over  it  with  a  camel's-hair  brush.  The  lymphocytes  ad- 
here to  the  brush.  Both  methods  (His,  6i)  may  be  applied  to  hardened 
sections  which  have  lain  in  water  for  a  day  or  so.  In  this  case,  how- 
ever, the  removal  of  the  lymphocytes  is  not  so  easy  as  in  fresh  sections. 

In  thick  sections  the  reticulum  is  hidden  by  the  lymphocytes. 
If,  on  the  other  hand,  very  thin  sections  (not  over  3  /ji)  be  made,  especially 
of  objects  fixed  in  Flemming's  solution,  the  adenoid  reticulum  stands  out 
clearly  without  any  further  manipulation. 

The  reticular  structure  may  also  be  demonstrated  by  an  artificial 
digestion  of  the  sections  with  trypsin.  The  sections  are  then  agitated  in 
water,  spread  on  a  slide,  dried,  then  moistened  with  a  picric  acid  solu- 
tion (i  gm.  in  15  c.c.  of  alcohol  and  30  c.c.  of  water),  again  dried,  cov- 
ered with  a  few  drops  of  fuchsin  S  solution  (fuchsin  S  i  gm.,  alcohol 
33  c.c,  water  66  c.c),  and  left  to  stand  for  half  an  hour.  The  fuchsin 
solution  is  then  carefully  removed,  the  section  washed  again  for  a  short 
time  in  the  same  picric  acid  solution,  then  treated  with  absolute  alcohol, 
xylol,  and  finally  mounted  in  Canada  balsam.  The  reticular  tissue  of 
both  lymphatic  glands  and  spleen  are  stained  a  beautiful  red  (F.  P. 
Mall).      (See  also  page  129.) 

The  treatment  of  splenic  tissue  is  practically  the  same  as  that  o^ 
the  lymphatic  glands. 

In  all  these  organs  (lymph-glands,  spleen,  and  bone-marrow)  a 
certain  amount  of  fluid  may  be  obtained  by  scraping  the  surface  of  the 
fresh  tissue.  This  may  then  be  examined  in  the  same  manner  as  blood 
and  lymph  (see  Technic  of  same).  Sections  of  lymph -glands  and  spleen 
previously  fixed  in  alcohol,  mercuric  chlorid,  or  even  in  Flemming's 
solution  may  be  examined  by  the  granula  methods  of  Ehrlich. 

By  using  the  chrome-silver  method  a  peculiar  network  of  retic- 
ular fibers  may  be  seen  in  the  spleen.      (Gitterfasern  ;   Oppel,  91.) 

The  examination  of  the  bone=marrow  belongs  also  to  this  chap- 
ter. The  marrow  of  the  diaphysis  is  taken  out  by  splitting  the  bone 
longitudinally  with  a  chisel.  With  a  little  practice,  it  is  easy  to  obtain 
small  pieces  of  the  marrow,  which  are  then  fixed  by  the  customary 
methods  and  cut  into  sections.  In  the  epiphysis  the  examination  is 
confined  either  to  the  pressing  out  of  a  small  quantity  of  fluid  with  a  vice, 
or  to  the  decalcification  of  small  masses  of  spongy  bone,  containing  red 
bone-marrow.  In  the  first  case,  methods  applicable  to  blood  examina- 
tion are  employed ;  in  the  second,  section  methods  (see  also  the  petrifi- 
cation method,  page  132)  are  used.  The  methods  given  for  the  prepara- 
tion of  lymph-glands  and  spleen  are  also  applicable  in  many  cases. 


THE    ORAL    CAVITY.  •  235 

TECHNIC  (QRCULATORY  SYSTEM). 

To  obtain  a  topographical  view  of  the  layers  composing  the 
heart  and  vessels,  sections  are  made  of  tissues  that  have  been  fixed  in 
Müller' s  fluid,  chromic  acid,  etc.  If  the  specimens  are  to  be  studied  in 
detail,  small  pieces  must  be  used,  and  are  best  fixed  in  chromic-osmic 
mixtures  or  corrosive  sublimate.  Celloidin  imbedding  is  recommended 
for  general  topographic  work.     The  further  treatment  is  elective. 

The  endothelium  of  the  intima  may  be  brought  to  view  by  silver 
nitrate  impregnation  methods,  by  injecting  silver  solutions  into  the  vascu- 
lar system.  The  endothelial  elements  of  the  smallest  vessels  and  capil- 
laries are  then  clearly  defined  by  lines  of  silver.  Larger  vessels  must 
be  cut  open,  the  intima  separated,  and  pieces  of  its  lamellae  examined. 

Elastic  elements,  plates  and  networks  are  best  observed  in  the 
tunica  media  of  the  vessels,  very  small  pieces  of  which  are  treated  for 
some  hours  with  33%  potassium  hydrate. 

The  appropriate  stains  for  sectionwork  are  those  which  bring 
out  the  elastic  elements  and  the  smooth  muscle-cells.  For  the  former, 
orcein  is  used. 

For  demonstrating  the  distribution  of  the  capillaries,  the  reader  is 
referred  to  the  injection  methods.  The  lymph -capillaries  are  injected 
by  puncture ;  compare  also  the  methods  of  Altmann. 


III.    THE  DIGESTIVE  ORGANS. 

The  intestinal  canal  with  the  glands  derived  therefrom  originates 
from  the  inner  layer  of  the  blastoderm,  the  entoderm.  The  latter, 
however,  does  not  extend  to  the  external  openings  of  the  body,  as 
the  ectoderm  forms  depressions  at  these  points  which  grow  inward 
toward  the  still  imperforate  fore  and  hind  gut  to  communicate 
finally  with  its  lumen.  This  applies  as  well  to  the  formation  of 
the  primitive  oral  cavity,  which  is  separated  only  secondarily  into 
oral  and  nasal  cavities,  as  to  the  anus.  The  anterior  boundary 
between  the  ectodermal  and  entodermal  portions  of  the  digestive 
tube  consists  of  a  plane  passing  through  the  opening  of  the  pos- 
terior nares  and  continued  downward  along  the  palatopharyngeal 
arch.  Everything  lying  anterior  to  this  is  of  ectodermal  origin, 
therefore  the  entire  oral  and  nasal  cavities  with  their  derivatives. 
The  lining  of  these  cavities  consists,  however,  of  a  true  mucous 
membrane,  closely  resembling  in  its  structure  that  of  the  intestinal 
tract. 


A.  THE  ORAL  CAVITY. 

The  epithelium  of  the  oral  mucous  membrane  is  of  the  stratified 
squamous  type,  differing  from  the  epithelium  of  the  epidermis 
in  that  the  stratum  granulosum  does  not  appear  here  as  an  inde- 
pendent  layer.     The   stratum   lucidum   is   also    wanting,   and    the 


236  •  THE    DIGESTIVE    ORGANS. 

cornification  of  the  layer  analogous  to  the  stratum  corneum  of  the 
skin  is  not  complete  (compare  Skin).  In  the  mucous  membrane 
the  cells  of  even  the  most  superficial  layers  contain  nuclei,  which, 
although  partly  atrophied,  still  show  chromatin,  and  as  a  conse- 
quence are  easily  demonstrated. 

Beneath  the  epithelium  lies  a  tissue  of  mesodermic  origin,  also 
belonging  to  the  mucous  membrane  and  known  as  the  mucosa  or 
stratum  proprium  (lamina  propria,  tunica  propria),  in  which  nu- 
merous glands  are  situated.  The  mucosa  consists  of  a  fibrillar 
connective  tissue  with  few  elastic  fibers,  and  of  adenoid  tissue 
containing  numerous  lymphoid  cells ;  essentially,  therefore,  a 
diffusely  distributed  adenoid  tissue  with  occasional  lymph-follicles 
imbedded  in  its  substance.  The  mucosa  presents  numerous 
papillae,  which  are  either  simple  or  compound  (branched)  eleva- 
tions of  the  mucosa,  varying  in  length  and  density,  according  to 
their  location  and  extending  for  variable  distances  into  the  over- 
lying epithelium.  As  in  the  papillary  layer  of  the  corium  (see 
Skin),  so  also  here  the  superficial  layer  of  the  stratum  proprium 
contains  very  fine  elastic  and  connective -tissue  elements  which  con- 
tribute to  the  structure  of  the  papillae.  All  these  papillae  contain 
capillaries  and  arterioles  which  are  derived  from  an  arterial  network 
in  the  mucosa.      The  lymphatics  are  similarly  arranged. 

At  the  red  margin  of  the  lips  the  papillae  are  unusually  high 
and  are  covered  at  their  summits  by  a  very  thin  epithelial  layer 
(Fig.  180).  Besides  the  sebaceous  glands  which  lie  at  the  angles 
of  the  mouth,  and  whose  ducts  open  at  the  surface,  there  are  here 
no  other  glandular  structures.  In  the  mucosa  of  the  mucous 
membrane  of  the  lips  and  cheeks  the  papillae  are  low  and  broad  ; 
here  also  open  the  ducts  of  compound  lobular,  alveolar  glands,  the 
glandules  labiales  and  buccales  whose  structure  is  similar  to  that  of 
the  large  salivary  glands  (see  these).  The  gums  possess  very  long 
and  attenuated  papillae,  covered  by  a  very  thin  layer  of  epithelium, 
therefore  bleeding  at  the  slightest  injury.  That  part  of  the  gum 
covering  the  tooth  has  no  papillae.  The  gums  contain  no  glands. 
The  papillae  of  the  hard  palate  are  arranged  obliquely,  with  their 
points  directed  toward  the  opening  of  the  mouth.  The  papillae  of 
the  soft  palate  are  very  low  and  may  even  be  absent.  They  are 
somewhat  higher  on  the  anterior  surface  of  the  uvula.  On  the 
posterior  surface  of  the  latter  occur  ciHated  epithelia  distributed  in 
islands  between  the  areas  of  stratified  squamous  epithelium.  In 
the  soft  palate  and  uvula  are  found  small  mucous  glands. 

Under  the  mucous  membrane  there  is  a  layer  consisting  princi- 
pally of  connective  tissue  and  elastic  fibers,  the  subinucosa  (stratum 
submucosum,  tela  submucosa).  In  the  mucous  membrane  of  the 
mouth  the  transition  of  the  tissue  of  the  mucosa  into  that  of  the 
submucosa  is  very  gradual.  The  submucosa  of  the  hard  palate  is 
closely  connected  with  the  periosteum  and  contains,  especially  at 
its  posterior  portion,  numerous  glands.      In   other  regions  of  the 


THE    ORAL    CAVITY. 


237 


mouth  (lip)  the  glands  extend  also  into  the  submucosa.  The 
mucosa  and  epithelium  lining  the  mouth  cavity  are  richly 
supplied  with  nerves  which  terminate  either  in  special  sensory 
nerve-endings  or  in  free  sensory  nerve-endings,  or  on  the  blood- 
vessels. In  the  papillae  of  the  mucosa  are  found  corpuscles  of 
Krause.  (See  p.  169.)  The  nerves  terminating  in  free  sensory 
endings  are  the  dendrites  of  sensory  neurones  (medullated  sensory 
nerves),  which,  while  yet  medullated,  branch  and  form  plexuses 
with  large  meshes,  situated  in  the  submucosa  and  deeper  portion  of 


Transitional  zone  with 
irregular  papillae. 


Epithe- 
1  i  u  m 
of  mu- 
cous 
mem- 
brane. 

Gland. 


Fig.   180. — Section  through  the  lower  lip  of  man  ;  X  ^^^ 


the  mucosa.  The  medullated  branches  of  the  nerve-fibers  constitut- 
ing these  plexuses  proceed  toward  the  epithelium,  dividing  further 
in  their  course.  Immediately  under  the  epithelium  the  medullated 
branches  lose  their  medullary  sheaths,  divide  further,  and  form  the 
subepithelial  plexuses.  The  nonmedullated  branches  enter  the 
epithelium,  where  they  form  telodendria  (end-brushes),  the  terminal 
branches  of  which  surround  the  epithelial  cells,  between  Avhich 
they  end  either  in  very  fine  granules  or  in  small  groups  of  such,  or, 
again,  in  variously  shaped  end-discs.      (See  Fig.  135.)     The  blood- 


238  THE    DIGESTIVE    ORGANS. 

vessels  are  richly  supplied  with  vasomotor  nerves,  the  neuraxes 
of  sympathetic  neurones,  which  terminate  on  the  muscle-cells  of 
the  vessels.  In  the  adventitia  are  also  found  free  sensory  nerve- 
endings.     (See  Fig.  177.) 

Ü  THE  TEETH. 

The  human  dentition  comprises  twenty  temporary  or  milk  teeth, 
namely,  above  and  below,  four  incisors,  two  canines,  and  four 
molars,  which  are  replaced  by  thirty-two  permanent  teeth,  con- 
sisting of  four  incisors,  two  canines,  four  premolars,  and  six  molars 
for  each  jaw.  Each  tooth  consists  of  a  crown,  which  projects  above 
the  gums,  a  relatively  short  and  narrowed  portion  known  as  the 
neck,  and  a  portion  which  fits  accurately  into  the  alveolus  and 
is  known  as  the  root.  For  the  variations  in  shape  which  the 
different  kinds  of  teeth  present,  the  reader  is  referred  to  the  text- 
books of  anatomy  or  to  special  works  dealing  with  this  subject. 

Structure  of  the  Adult  Tooth. — The  adult  tooth  is  made  up 
of  three  substances — the  enamel,  the  dentin,  and  the  cementum.  The 
latter  covers  that  part  of  the  tooth  within  the  alveolar  process  of 
the  jaw  and  also  the  root  of  the  tooth.  The  enamel  caps  that  part 
of  the  tooth  projecting  into  the  oral  cavity,  the  crown  of  the  tooth. 
The  neck  of  the  tooth  is  the  region  where  the  cementum  and 
enamel  come  in  contact.  The  greater  part  of  the  tooth  consists  of 
dentin,  which  is  present  in  the  crown  as  well  as  in  the  root.  All 
the  substances  of  the  tooth  just  mentioned  become  very  hard  from 
the  deposition  of  lime -salts.  Every  tooth  contains  a  cavity  sur- 
rounded by  dentin,  the  pulp  cavity,  or  dental  cavity.  This  is  filled 
with  a  soft  tissue,  the  pulp,  consisting  of  white  fibrous  tissue,  ves- 
sels, and  nerves.  That  part  of  the  pulp  cavity  lying  in  the  axis  of 
the  fang  is  called  the  root-canal ;  by  an  opening  in  the  latter  (fora- 
men apicis  dentis)  the  pulp  is  connected  with  the  periosteal  con- 
nective tissue  of  the  dental  alveolus. 

The  enamel  is  a  very  hard  substance,  the  hardest  in  the  body, 
and  may  be  compared  to  quartz.  In  uninjured  teeth  the  enamel  is 
covered  by  an  exceedingly  thin,  structureless  membrane,  the  cuti- 
cula  dentis  or  Nasmyth's  membrane,  which  varies  in  thickness, 
measuring  from  o.g  jut  to  1.8  fx.  It  is  very  resistant  to  acids  and 
alkalies.  On  its  under  surface  it  often  shows  small  pits,  into  which 
project  the  ends  of  the  enamel  prisms.  The  enamel  contains  very 
little  organic  substance  (from  3^  to  5  ^),  in  consequence  of  which 
it  is  soluble  in  acids  with  scarcely  any  residue.  The  elements 
composing  it  are  prismatic  columns,  the  enamel  prisms,  which 
probably  occupy  the  whole  thickness  of  the  enamel  from  the 
superficial  membrane  to  the  dentin.  They  are  slightly  thicker  at 
the  surface  of  the  tooth  than  at  the  dentin,  and  in  transverse 
section  show  a  hexagonal  or  polygonal  shape,  and  measure 
from    3   //  to  6  //  in   diameter.     They   often  show  quite  regular 


THE    TEETH. 


239 


~   Enamel. 


Pulp  cavity. 


transverse  markings  which  express,  however,  no  structural  pecu- 
liarity, but  are  due  to  irregularities  in  the  prisms.  They  are 
joined  to  each  other  by  a  cement-substance  which  is  somewhat 
more  resistant  than  the  substance  of  the  prisms  themselves.  In  the 
adult  they  are  entirely  homogeneous,  but  in  embryos  and  even  in 
the  new-born  they  show  a  (fibrillar)  longitudinal  striation.  In  their 
course  through  the  thickness  of  the  enamel  they  change  their 
direction  by  a  series  of 
symmetrical  curves,  and 
cross  each  other  in  groups 
ina  typical  manner.  There 
are  also  seen  in  the  enamel 
the  parallel  lines  known  as 
the  lines  of  Retzius  (see 
Fig.  181),  which  pass 
obHquely  through  the 
enamel  and  which  are  to 
be  regarded  as  traces  of 
the  strata  caused  by  the 
periodic  deposition  of  lime- 
salts  ;  they  are  very  vari- 
able, as  their  structure 
depends  on  the  nutritive 
condition  during  the  depo- 
sition of  the  lime  -  salts 
(Berten).  Another  series 
of  parallel  or  nearly  par- 
allel stripes  or  lines,  known 
as  Schräger  s  lines,  are 
also  observed.  Those  in 
the  lateral  portions  of  the 
enamel  have  a  direction 
nearly  perpendicular  to 
the  surface.  They  are 
thought  to  be  due  to  a 
difference  in  the  refraction 
of  the  light,  presented  by 
bundles  or  layers  of  enamel 
prisms  so  disposed  as  to  be 
cut  in  different  directions. 
The  dentin  is,  next  to 
the  enamel,  the  hardest 
tissue  of  the  tooth.  After 
decalcification   it   presents 

a  ground  substance  in  which  are  found  numerous  very  fine  fibrils, 
which  do  not  branch  nor  anastomose,  and  are  in  their  behavior 
toward  acids  and  alkalies  like  the  fibrils  of  white  fibrous  (collagenous) 
tissue.      They  yield  gelatin  on  boiling.      The  fibrils  are  separated  by 


Dentin. 


Cementum. 


Fig.  181. — Scheme  of  a  longitudinal  section 
through  a  human  tooth.  In  the  enamel  are  seen 
the  "lines  of  Retzius." 


240 


THE    DIGESTIVE    ORGANS. 


an  interfibrillar  substance,  in  which  the  mineral  salts  are  deposited. 
The  course  of  the  fibrils  is,  in  the  main,  parallel  to  the  surface  of 
the  dentin.  They  are  often  grouped  in  small  bundles  (v.  Ebner). 
The  dentin  is  permeated  by  a  system  of  canals  having  usually  a 
transverse  direction,  the  so-called  dentinal  hibules,  which  are  from 
1.3  /-^  to  4.5  fx  in  diameter.  These  originate  in  the  pulp  cavity,  and 
during  their  course  become  slightly  curved,  like  the  letter  S-  The 
dentinal  tubules  usually  present  several  dichotomous  divisions  near 
their  origin,  then  pass  to  the  outer  third  of  the  dentin  without 
conspicuous  divisions ;  here  they  again  branch,  becoming  constantly 
smaller.     In  their  course  they  give  off  numerous  side  twigs  which 


Interglobular     ^^ 
space.  ^ 


[  ■  ■  —  Enamel. 


Branching  of  the 
dentinal  tubules. 


—  Dentinal  tubules. 


Fig.  182. — A  portion  of  a  ground  tooth  from  man,  showing  enamel  and  dentin  ;   X  ^TO- 


anastomose  with  those  of  neighboring  tubules.  The  general  course  of 
these  tubules  is  shown  in  figure  181.  Certain  of  the  tubules  pass 
for  a  short  distance  into  the  enamel,  where  they  are  found  between 
the  prisms.  In  the  human  tooth  the  majority  end  just  before  reach- 
ing the  enamel.  In  the  root  of  the  tooth  they  end  near  the  surface, 
or  in  the  interglobular  spaces  (see  below),  or,  again,  they  may  be 
joined  to  form  loops.  The  dentinal  tubules  possess  sheaths,  the 
sheaths  of  Neumann,  which  may  be  isolated,  analogous  to  the 
sheaths  of  the  canaliculi  of  bone.  They  may  be  regarded  as  differ- 
entiated and  more  resistant  ground  substance.  The  dentinal  tubules 
contain  throughout  their  entire  length  filiform  prolongations  of  cer- 
tain pulp-cells  (odontoblasts),  the  dejitmal  fibers.      Peculiar,  irregu- 


THE    TEETH. 


241 


larly  branched  spaces  are  often  seen  in  the  dentin.  These  are  the 
interglobular  spaces  of  Czermak.  They  represent  areas  in  which 
calcification  has  not  taken  place.  Their  number  is  variable  ;  when 
relatively  small  and  numerous,  they  appear,  in  dry  preparations  seen 
under  low  magnification,  as  a  granular  layer — the  granular  layer  of 
Tomes. 

The  cementum  is  closely  adherent  to  the  dentin,  and  consists  of 


Fig.  183. — A,  Longitudinal  section  through  a  human  molar  from  the  center  of  the 
enamel  layer,  decalcified  with  dilute  hydrochloric  acid ;  B,  tangential,  C,  radiate,  and 
D,  transverse  section  through  the  dentin  of  a  human  tooth,  showing  the  fibrillar  struc- 
ture of  the  ground-substance  (taken  from  v.  Ebner,  91)  :  a  and  b.  Two  layers  in  which 
the  direction  of  the  enamel  prisms  changes ;  in  <:  is  seen  a  dentinal  fiber  with  its  sheath  ; 
e,  groups  of  fibrils ;  d,  dentinal  tubules. 


bone  tissue,  the  parallel  lamellae  of  which  contain,  as  a  rule,  no 
Haversian  canals.  There  occur,  however,  cement  lamellae,  which 
in  places  lose  their  bone-cells.  A  peculiarity  of  the  cementum  is 
the  presence  of  a  large  number  of  Sharpey's  fibers,  which  are 
especially  abundant  in  those  areas  containing  no  bone-corpuscles. 
These  fibers  are  usually  found  in  an  uncalcified  condition. 

The  tooth-pulp  is  a  tissue  resembling  embryonic  connective 
tissue,  consisting  of  connective-tissue  fibrils,  branched  connective- 
tissue  cells,  and  a  semifluid,  interfibrillar  ground-substance.  It  is 
characteristic  of  this  tissue  that  the  fibrils  never  join  to  form  con- 
nective-tissue fibers.  It  is  probable  that  the  fibrils  are  similar  to 
those  of  white  fibrous  (collagenous)  connective  tissue  (possibly  retic- 
ular fibers),  although  there  is  a  difference  of  opinion  as  concerns 
this  point,  by  observers  who  have  given  it  special  attention  (see 
V.  Ebner,  Rose).  At  the  surface  of  the  pulp  is  a  continuous  layer 
of  cells,  the  odontoblasts.  These  are  columnar  cells  with  basal 
16 


242  THE    DIGESTIVE    ORGANS. 

nuclei  and  two  or  three  processes  extending  into  the  canaliculi  of 
the  dentin,  forming  here  the  dentinal  fibers  already  described.  As 
a  rule,  the  odontoblasts  also  send  a  single  fiber  into  the  pulp. 
These  may  intertwine  and  give  rise  to  a  network  within  its  sub- 
stance. 

Peridental  MembraJie,  Alveolar  Periosteiwt. — The  tooth  is  joined 
to  the  alveolus  by  a  fibrous  tissue  membrane,  the  peridental  mem- 
brane or  alveolar  periosteum,  which  represents  the  periosteum  of 
the  alveolus  and  the  cementum  of  the  tooth.  This  consists  of 
bundles  of  connective  tissue  (elastic  fibers  are  here  absent)  directly 
continuous  with  Sharpey's  fibers  in  the  cementum  and  the  alveolus. 
Between  these  coarser  bundles  of  fibers,  which  have  a  direction 
nearly  horizontal  in  the  upper  portions  of  the  peridental  membrane 
and  incline  toward  the  lower  end  of  the  tooth  in  its  lower  f)ortion, 
there  is  found  a  looser  connective  tissue,  containing  numerous 
nerve-fibers,  blood-vessels,  and  peculiar  masses  of  epithelial  cells 
representing  the  remains  of  the  enamel  organs,  to  be  described 
later.  These  epithelial  remains  have  by  some  observers  been 
regarded  as  glandular  in  nature;  further  observation  is,  however, 
needed  before  this  can  be  accepted  as  proved.  At  the  apex  of  the 
root  there  is  found  a  less  dense  connective  tissue,  continuous  with 
that  of  the  tooth  pulp.  At  the  neck  of  the  tooth  the  peridental 
membrane  disappears  in  the  submucosa  of  the  gum. 

The  blood-vessels  of  the  teeth  have  been  fully  described  by 
Lepowsky,  who  has  studied  them  in  a  number  of  mammals,  and  in 
man  in  embryos  and  in  full  development ;  his  account  is  here  fol- 
lowed. The  artery,  accompanied  by  the  veins,  enters  through  the 
apical  foramen,  passes  up  through  the  pulp,  dividing  into  branches 
as  it  reaches  the  upper  portion  of  the  pulp  cavity;  these  branches 
are  spread  out  fan-shaped  and  after  further  division  and  the  forma- 
tion of  capillaries,  end  in  capillaries  which  are  situated  between  the 
layer  of  odontoblasts  and  the  dentin,  forming  here  a  capillary  plexus 
which  presents  narrow  meshes,  in  regions  where  the  odontoblasts 
are  most  active. 

There  are  in  all  probability  no  lymphatic  vessels  in  the 
pulp. 

Numerous  medullated  nerve-ßbers  (dendrites  of  sensory  neurones) 
enter  the  pulp  cavity  through  the  apical  foramen.  Some  of  these 
lose  their  medullary  sheaths  soon  after  entering,  or  just  before 
entering,  the  pulp,  and  divide  into  long,  fine,  varicose  fibers  which 
interlace  to  form  a  loose  plexus  under  the  odontoblasts.  Other 
medullated  fibers,  grouped  into  small  bundles,  ascend  in  the  pulp 
for  variable  distances  ;  the  nerve -fibers  of  the  bundles  then  sepa- 
rate and  as  single  fibers  approach  the  superficial  portion  of  the 
pulp,  and,  after  losing  their  medullary  sheaths,  divide  into  fine 
varicose  fibers  forming  under  the  odontoblasts  a  plexus  continuous 
with  the  plexus  above  mentioned.      From  the  varicose  nerve-fibers 


THE    TEETH. 


243 


of  this  plexus  small  terminal  branches  are  given  off  which  termi- 
nate between  the  odontoblasts,  or  pass  through  the  layer  of 
odontoblasts,  to  end  between  these  and  the  dentin  (Retzius,  94  ; 
Huber,  98;  Rygge,  1902).  Medullated  nerve-fibers  also  terminate 
in  free  endings  in  the  peridental  membrane. 

Development  of  the  Teeth. — In  the  second  month  of  fetal 
life  the  first  traces  of  the  teeth  are  seen  in  the  development  of  a 
groove  along  the  inner  edge  of  the  fetal  jaw,  the  dentinal  or  en- 
amel groove.  From  the  floor  of  the  latter  an  epithelial  ridge 
is  formed  constituting  the  anläge  of  the  enamel  organs  and 
known  as  the  dentinal  ridge,  or  enamel  ledge.  At  those  points 
at  which  the  milk-teeth  later  appear,  the  enamel  ledge  develops 
solid  protuberances  corre- 
sponding in  number  to  the 
temporary  teeth.  These  are 
known  as  the  dentinal  bulbs 
or  enamel  germs.  In  their 
first  stage  of  development 
the  enamel  germs  are  knob- 
like, but  later  their  bases 
spread,  and  they  become 
flattened  and  finally  cup- 
shaped  by  the  pushing  up 
into  them  of  connective  - 
tissue  projections,  the  den- 
tinal papillce.  At  the  same 
time    they   gradually    sink 


Cementum.  <^ 


Dentin.  < 


Fig.  184. — Cross-section  of  human  tooth, 
showing  cement  and  dentin;  X  212.  At  a  are 
seen  small  interglobular  spaces  (Tomes'  granular 
layer). 


deeper  into  the  underlying 
tissue,  but  still  remain  con- 
nected, by  means  of  a  thin 
cord,  with  the  epithelium  of 
the  enamel  ledge,  which  now  lies  on  the  inner  side  of  the  enamel 
germs.  The  enamel  germs  now  differentiate  into  enamel  organs. 
In  this  stage  they  consist  of  an  outer  layer  of  columnar  epithelial 
cells,  which  are  to  be-^  regarded  as  a  direct  continuation  of  the  basal 
cells  from  the  epithelium  of  the  oral  mucous  membrane,  or  still 
better,  of  the  enamel  ledge  ;  the  epithelium  in  the  interior  of  the 
organ  is  derived  from  the  stratum  Malpighii  of  the  oral  epithe- 
lium. The  cells  of  this  layer,  however,  undergo  a  change  in 
shape  and  structure,  in  that  an  increased  quantity  of  lymph-plasma 
or  intercellular  substance  collects  in  the  interspinous  spaces  between 
the  cells,  pushing  the  cells  apart,  and  allowing  their  processes  to 
develop  until  the  cells  finally  assume  a  stellate  shape.  In  this  way 
the  enamel  pulp  is  gradually  formed.  The  next  stage  is  character- 
ized by  a  vertical  growth  of  the  dentinal  papillae,  which  soon  be- 
come surrounded  on  all  sides  by  the  cap-like  enamel  organs.  The 
cyhndric  cells  (enamel  cells)   of  the   enamel  organs   lying  next  to 


244  THE    DIGESTIVE    ORGANS. 

the  papillae  become  lengthened,  and  after  passing  through  further 
changes,  finally  develop  into  the  enamel  prisms  of  the  teeth.  At 
the  periphery  of  the  dentinal  papillae,  there  is  differentiated  a  layer 
of  columnar  cells,  the  odontoblasts,  which  have  a  connective-tissue 
origin,  and  later  form  the  dentin.  During  these  processes  a 
connective -tissue  mantle,  the  dental  sac,  rich  in  cellular  and  fibrous 
elements,  is  formed  around  each  tooth  anläge. 

The  earliest  appearance  of  the  enamel  is  in  the  form  of  a  cuticu- 
lar  membrane,  developed  from  the  ends  of  the  enamel  cells  resting 
on  the  dentinal  papilla,  this  cuticular  membrane  appearing  in  the  form 
of  a  thin  layer  covering  the  top  of  the  dentinal  papilla.  Some  time 
later,    short  striated    processes — Tomes'    processes — appear  on  the 


J Odontoblasts. 

Odontoblasts.     


Terminal  nerve- 
fiber. 

Terminal  nerve- 
fiber. 


Fig.  185. — Nerve  termination  in  the  pulp  of  a  rabbit's  molar,  stained  in  methylene- 
blue  {intra  vitam)  :  a.  Odontoblasts  seen  in  side  view  ;  b,  a  number  of  odontoblasts  seen 
in  end  view,  showing  a  terminal  branch  of  a  nerve-fiber  situated  between  the  odonto- 
blasts and  the  dentin    (Huber,  "Dental  Cosmos,"  October,  1898). 

lower  end  of  each  of  the  enamel  cells  (the  end  toward  the  dentinal 
papilla).  These  are  imbedded  in  a  cement-substance,  forming  a 
continuous  layer.  The  Tomes'  processes  are  regarded  as  the  be- 
ginnings of  the  enamel  prisms.  Calcification  begins  in  the  middle 
of  these  processes  ;  they  thicken  at  the  expense  of  the  cement- 
substance  surrounding  them,  which  later  also  calcifies.  The  enamel 
as  a  whole  thickens  by  the  elongation  of  th©  Tomes'  processes  of 
the  enamel  cells  and  by  their  subsequent  calcification.  The  process 
ends  finally  in  the  death  and  partial  absorption  of  the  enamel  cells 
and  the  remaining  elements  of  the  enamel  organs  ;  these  structures 
persist  for  a  short  time  after  the  eruption  of  the  tooth  as  a  cuticular 
sheath. 

The  dentin  is  developed  by  the  odontoblasts  by  a  process 
analogous  to  that  observed  in  the  formation  of  bone  by  the  osteo- 
blasts. These  epithelioid  cells  secrete  at  their  outer  surfaces  a 
homogeneous  substance  which  fuses  to  form  a  continuous  layer, 
the  ^nembrana  prceformativa.  The  further  development  of  the  dentin 
is  as  follows  :  Its  ground-substance  is  deposited  at  the  cost  of  the 
lateral  portions  of  the  odontoblasts  (under  the  membrana  praeforma- 


Fig.  iS6. 


Fig.  187. 


<fi'^'—   P 


Fig.  I 


Fies  186-18Q.— Four  stages  in  the  development  of  a  tooth  in  a  sheep  embryo  (from 
the  lower  jaw)  ;  Fig.  186,  Anlage  of  the  enamel  germ  connected  with  the  oral  ep.thehum 
hv  the  enimel  led-e  ;  Fig.  iSyf  first  trace  of  the  dentinal  papilla;  Fig.  188,  advanced 
stCwlA^rgeTfa^illa^nd  d^  enamel  pulp  ;   Fig.  189    buddmg  from  the 

enamel  ledge  of  the  anläge  of  the  enamel  germ,  which  later  goes  to  form  the  enamel  of 
r^em^aneSt  tooth;  at  the  periphery  of  the  papilla  the  odontoblasts  -^  begin  mng  to 
differentiate.  Figs.  186,  187,  and  188,  X  "O  ;  Fig.  189,  X  40..  «'«'-';'  f^'^f^^^ 
of  the  oral  cavity;  b,  b,  b,  b,  its  basal  layer;  c,  c,  c,  the  superficial  cells  of  the  enamel 
organ  ;Tk./,  I,  enln^el  pulp  ;  /,  A  /,  dentinal  papilla  ;  s,  s,  enamel-  ormmg  element 
(enamel  cells)  ;  0,  odontoblasts  ;  S,  enamel  germ  of  the  permanent  tooth  ;  v,  part  ot  the 
enamel  ledge  of  a  temporary  tooth  ;  u,  surrounding  connective  tissue. 


246 


THE    DIGESTIVE    ORGANS. 


~  Enamel  pulp. 


Enamel  cells. 


V^*t->'-^'°'S*-™^ 


b 


-~  Odontoblasts. 


tiva),  the  axial  portion  of  the  cells  remaining  intact  as  the  dentinal 
fibers  ;  the  basal  portions  of  the  cells  containing  the  nuclei  persist, 
later  constituting  the  odontoblasts  of  the  adult  pulp.  By  the  fusion 
of  the  segments  of  the  ground-substance  formed  by  each  cell,  it 
becomes  a  homogeneous  mass,  but  soon  displays  connective-tissue 
fibrils  which  gradually  undergo  a  process  of  calcification.  The  mem- 

brana  praeformativa  has 
no  fibers  and  calcifies 
much  later.  It  lies  im- 
mediately beneath  the 
enamel  or  the  cementum, 
and  in  the  normal  tooth 
always  contains  small  in- 
terglobular spaces.  In 
the  adult  tooth  this  mem- 
brane in  its  entirety  is 
known  as  Tomes'  gran- 
ular layer. 

The  cementum  is 
merely  a  periosteal 
growth  of  bone  originat- 
ing in  the  tissue  of  the 
dental  sac  and  adhering 
to  the  dentin.  Although 
at  first  the  enamel  or- 
gan almost  entirely  sur- 
rounds the  dentinal  pa- 
pilla, later  a  portion  of 
that  part  of  it  in  the  re- 
gion of  the  fang  is  ab- 
sorbed in  order  to  allow 
the  cementum  to  reach 
the  surface  of  the  dentin. 
Remains  of  this  regressive  portion  persist  as  the  epithehal  nests  of 
the  dental  root  (compare  p.  242). 

The  contents  of  the  dentinal  papillae  change  into  the  tissue  of  the 
dental  pulp.     , 

As  early  as  the  third  month  outgrowths  appear  on  the  inner 
side  of  the  enamel  ledge  next  to  the  partly  developed  milk-teeth, 
which  represent  the  anlagen  of  the  enamel  organs  of  the  permanent 
teeth.  Their  further  development  is  similar  to  that  of  the  milk  teeth. 
The  enamel  organs  of  the  molars  are  also  developed  from  an  enamel 
ledge  which  is  practically  a  backward  continuation  of  the  embryonic 
enamel  ledge.  With  their  crowns  presenting,  the  temporary  teeth 
at  last  break  through  the  epithelium  of  the  gums.  When  the  de- 
velopment of  the  permanent  teeth  is  so  far  advanced  that  they  are 
ready  to-  perforate,  regressive  processes  begin  at  the  roots  of  the 


% 


®N    Q 


Fig.  igo. — A  portion  of  a  cross-section  through 
a  developing  tooth  (later  stage  than  in  Fig.  189)  ; 
X  720  :  The  dentin  is  formed,  but  has  become  homo- 
geneous from  calcification.  Bleu  de  Lyon  differen- 
tiates it  into  zones  {a  and  b).  At  c  is  seen  the  in- 
timate relationship  of  the  odontoblasts  to  the  tissue  of 
the  dental  pulp. 


THE    ORAL    CAVITY. 


247 


milk-teeth,  which  are  due,  as  in   Hke  conditions  of  the  bone   to  the 
action  of  certain    cells,  which   are  here  known  as  "  odontoclasts 
The  crowns  of  the  milk-teeth  are  then  thrown  off,  one  by  one,  by 
the  growing  permanent  teeth.  ,     ,    .      ,       1 

For  further  information  as  to  the  teeth  and  their  development, 
see  the  articles  by  v.  Ebner  (Scheff 's  -  Handbuch  der  Zahnheil- 
kunde"  and  in  KöUiker's  "Handbuch  der  Gewebelehre,  Bd.  ni), 
whose  studies  we  have  to  a  great  extent  followed  on  this  subject. 


2.  THE  TONGUE. 
The    Lingual  Mucous  Membrane   and  its  Papillae.— The 

mucous  membrane  of  the  tongue  differs  in  general  very  little  from 


?'n,^!i^-."-- 


ävvi'A''^^^^' 


'»'*'S' 


Fig.   191. — Fungiform  papilla  from  human  tongue. 

that  lining  the  rest  of  the  oral  cavity.  It  must,  however,  be  borne 
in  mind  that  in  the  greater  part  of  the  tongue  the  submucosa  is 
poorly  developed,  and  as  a  consequence  the  mucous  membrane  on 
the  upper  surface  and  base  of  the  tongue  is  scarcely  movable. 
Other  peculiarities  of  the  lingual  mucous  membrane  are  the  absence 
of  glands  in  the  mucosa  on  the  upper  surface  of  the  tongue,-- 
although  glands  are  found  in  the  musculature  of  the  tongue,  their 
ducts  passing  through  the  mucosa,— the  presence  of  epithelial 
papilla;,  and  of  lymph-follicles  at  the  base  of  the  tongue. 

The  upper  surface  of  the  tongue  is  roughened  by  the  presence 
of  epithelial  projections,  the  lingual  pa  pill cb.  The  latter  are  almost 
entirely  epithelial  structures,  and  should  not  be  confused  with  those 
papillae  which  are  composed  exclusively  of  connective  tissue.      There 


248 


THE    DIGESTIVE    ORGANS. 


are  several  classes  of  lingual  papillae — the  filiform,  the  fungiform, 
and  the  circumvallate  papillae.  The  most  numerous  are  the  thread- 
like or  filiform  papillcB  (from  0.7  to  3  mm.  long).  These  are  scat- 
tered over  the  entire  upper  surface  of  the  tongue,  and  consist  of 
conic  projections  of  the  epithelium  and  of  the  mucosa.  The  con- 
nective-tissue portions  of  these  papillae  are  very  thin  and  long.  The 
basal  layers  of  the  epithelium  can  not  be  distinguished  from  the 
same  layers  covering  the  surrounding  mucosa,  but  the  more  super- 


Papilla  filiformis. 


MA  .  3-<=    •> 


Tongue  epithe- 
lium. 


Connective-tissue 
papilla. 


'YAH 


''  K 


^^^V^^V^, 


^_    _.'  __i14^-^".>4]^L4    Mucosa. 


Basal  epithelial 
layer. 


Fig.  192, — From  a  cross-section  of  the  human  tongue,  showing  short,  thread-like  papillae 

(filiform)  ;   X  ^4°. 


ficial  layers  are  differentiated,  in  that  their  cells  are  arranged  parallel 
to  the  long  axes  of  the  papillae  and  overlap  each  other  like  tiles 
(Fig.  192).  Their  free  ends  are  often  continued  into  several  spine- 
like processes.  Less  numerous  than  the  filiform  are  the  fungiform 
papillcB  (from  0.7  to  1.8  mm.  in  height)  scattered  here  and  there 
between  the  former.  They  are  nearly  hemispheric  in  shape,  and  are 
joined  to  the  surface  of  the  tongue  by  a  slightly  constricted  base. 
At  times  they  are  even  partly  sunk  into  the  mucous  membrane. 
The  mucosa  is  raised  under  the  epithelium  to  form  connective -tissue 
papillae  (Fig.  191).     On  the  free  surface  of  the  fungiform  papillae 


THE   ORAL   CAVITY. 


249 


are  sometimes  found  taste-buds,  or  taste-goblets,  which  He  im- 
bedded in  the  epithehum  and  extend  through  its  entire  thickness. 
The  circuuivallate  papillce  occupy  a  definite  region  on  the  upper 
surface  of  the  tongue,  and  are  arranged  in  two  rows,  forming 
almost  a  right  angle,  with  the  apex  directed  backward  and  situated 
just  in  front  of  the  foramen  caecum  (Morgagni).  These  papillae 
are  few  in  number,  about  eight  to  fifteen  in  all.  In  shape  they 
are  similar  to  those  of  the  fungiform  type,  but  are  much  larger 
(about  I  or  2  mm.  in  diameter),  and  sunk  so  deeply  into  the 
mucous  membrane  that  the  latter  forms  a  wall  around  their  sides. 
Here  also  the  mucosa  passes  up  into  the  papillae  and  forms  con- 
nective-tissue papillae  of  its  own  at  the  upper  surface,  while  at  the 
sides  it  merely  adheres  to  the  smooth  inner  surface  of  the  epithelial 
layer.  Taste-buds  are  found  in  the  epithelium  at  the  sides  of  the 
papillae,  and  also  in  that  of  the  ridges  surrounding  the  papillae.  At 
the  sides  of  the  human  tongue  and  near  its  base  are  the  so-called 
fimbri(B  lingua.      These  are  irregular  folds  of  mucous  membrane, 


,r;-'f^^-'-^- 

^:^^^m-  ^ 

p 

-^ 

.  .''j        ;■,    ■      '  '            -~^    '■: 

;.::^: -;.■    ■     'v.   •-''. 

"-   _  . 

■f'\ 

"-     ^     -■     -          ""-'■"',-                '   - 

'    , 

•  •' 

' 'i  :■'   ^--^-X 

., 

'-V-'    ■"  -        ~  -'J:  "■--■■  '-■ 

Fig.   193, — Longitudinal  section  of  foliate  papilla  of  rabbit,  showing  taste-buds. 


the  sides  of  which  also  contain  taste-buds.  In  the  rabbit  they  are 
more  regular  in  structure  and  consist  of  parallel  folds  of  mucous 
membrane  thickly  dotted  with  taste-buds,  and  are  termed  the  foliate 
papillcB."  In  place  of  the  circumvallate  papillae,  the  guinea-pig  pos- 
sesses structures  similar  to  the  foliate  papillae  of  the  rabbit. 

Into  the  depressions  in  which  the  circumvallate  papillae  lie  and 
into  those  between  the  folds  of  the  fimbriae  linguae  open  the  ducts 
of  numerous  serous  glands,  the  glands  of  v.  Ebner  (see  below). 

The  Taste-buds. — The  gustatory  organs  in  the  form  of  taste- 
buds  are  found  on  the  surface  of  the  tongue,  principally  on 
the  lateral  surfaces  of  the  circumvallate  papillae  and  the  fimbriae 
linguae  (foliate  papillae).  They  are  also  occasionally  met  with  in 
the  epithelium  of  the  fungiform  papillae  and  the  soft  palate,  and  on 
the  posterior  surface  of  the  epiglottis.  They  always  lie  imbedded 
in  the  epithelium  and  extend  through  its  entire  thickness  ;  they  are 
ovoid  in  form,  with   base   downward  and  the  smaller  pole  at  the 


250 


THE    DIGESTIVE    ORGANS. 


surface.  The  whole  structure  is  surrounded  by  the  epitheHum  of 
the  mucous  membrane  of  the  regions  in  which  they  occur,  except 
at  the  attenuated  outer  end  of  the  taste-bud,  where,  by  means  of  a 
small  opening,  the  taste-pore,  it  communicates  with  the  oral  cav- 
ity., Most  of  the  cells  constituting  the  taste-buds  are  elongated, 
spindle-shaped  structures,  extending  from  one  end  of  the  organ  to 
the  other,  with  spaces  between  them.  There  are  four  varieties  of 
these  cells  :  (i)  The  outer  sustentacular  or  tegmental  cells,  lying  at 
the  periphery  of  the  organ  with  a  nucleus  in  their  center,  and 
having  a  short,  cone-shaped  cuticular  projection  ;  (2)  the  inner 
sustentacular  or  rod-shaped  cells,  which  are  more  slender  structures 
with  basally  situated  nuclei  and  without  a  cuticular  projection  ; 
between  the  latter  are  (3)  elongated,  spindle-shaped,  neuro-epithe- 


Epithelium.  — 


Ebner's 
gland. 


Fig.  194. — Longitudinal  section  of  a  human  circumvallate  papilla;  X^o. 

lial  cells,  with  the  nucleus  of  each  in  the  thickest  portion  of  the 
cell,  and  with  slender,  stiff  processes  projecting  into  the  taste -pore  ; 
(4)  a  few  broad  basal  cells,  communicating  with  each  other  as  well 
as  with  the  sustentacular  cells  by  numerous  processes.  We  have, 
therefore,  in  the  cells  of  the  first,  second,  and  probably  fourth 
varieties,  elements  which  belong  exclusively  to  the  sustentacular 
apparatus  of  the  organ  (Hermann,  85,  88). 

Von  Ebner  found  in  the  taste-buds  of  the  circumvallate  papillae 
of  man,  monkey,  and  cat,  as  well  as  of  the  papillae  foliatae  of  the 
rabbit,  an  open  space  situated  between  the  taste-pore  and  the  tip 
of  the  taste-bud  (Fig.  195).  These  spaces  vary  according  to  the 
species,  and  are  bounded  above  by  the  summits  of  the  tegmental 
cells  and  laterally  and  below  by  the  more   centrally  situated  sus- 


THE    ORAL   CAVITY. 


251 


Epithe-    Nerve- 
Hum,      fibrils. 


Process  of 
iieuro-epi 

thelial      Taste- 
cell,  pore. 


tentacular  cells.  The  cavities  are  often  10  [i  in  depth,  and  are 
filled  with  a  fluid  apparently  in  communication  with  the  fluid  of 
the  depression  into  which  the  circumvallate  papillae  are  sunk.  The 
processes  of  the  neuro-epithelial  cells  project  into  the  cavity  from 
its  floor  and  lateral  walls,  but  do  not  extend  as  far  as  the  taste- 
pore. 

The  circumvallate  papillae  are  differentiated  from  the  adjacent 
surface  of  the  tongue  by  the  development  of  a  solid  encircling 
epithelial  ridge.  Nu- 
merous taste -buds  ap- 
pear on  the  surface 
quite  early  in  the  his- 
tory of  the  embryo. 
These,  however,  dis- 
appear completely 
when  the  permanent 
taste  -  buds  develop 
from  the  basal  cells 
of  the  epithelial  ridge. 
Similar  phenomena 
occur  in  the  fungiform 
papillae  ( Hermann, 
88). 

The  neural  epith- 
elia  of  the  taste-gob- 
lets were  formerly  re- 
garded as  directly 
connected    with     the 

nerve-fibers  by  means  of  long  processes,  but  the  latest  researches 
have  shown  that  dendrites  of  sensory  neurones  (sensory  nerves) 
enter  the  taste-buds  and  end  free  in  telodendria.  The  latter  sur- 
round the  neuro-epithelial  and,  to  some  extent,  the  sustentacular 
cells,  their  relations  depending  upon  contact. 

The  Lymph-follicles  of  the  Tongue  (Folliculi  linguales) 
and  the  Tonsils. — At  the  root  of  the  tongue,  and  especially  at  its 
sides,  are  numerous  elevations  due  to  the  increased  quantity  of 
lymphoid  tissue  found  in  the  mucosa  of  these  regions,  the  lingual 
tonsils,  or  lingual  follicles.  In  the  center  of  each  follicle  is  a  cavity 
communicating  with  the  exterior  and  caused  by  an  invagination  of 
the  epithelium.  The  lymphoid  tissue  contains  a  number  of  more  or 
less  distinctly  defined  lymph-nodules,  some  even  showing  germ 
centers  {znd.  p.  197).  The  whole  structure  is  surrounded  by  a 
connective -tissue  capsule.  The  epithelial  walls  of  the  follicular 
cavities  often  show  extensive  degenerative  changes,  which  are 
accompanied  by  increased  migration  of  leucocytes  into  the  oral 
cavity.  These  leucocytes  change  (according  to  Stohr,  84)  into  the 
so-called  mucous  or  salivary  corpuscles  of  the  saliva. 

Pharyngeal  Tonsil. — The  pharyngeal  tonsils  may  be  regarded 


Terminal 
branches  of 
nerves. 


Fig.  195. — Schematic   representation   of   a  taste-goblet 
(partly  after  Hermann,  88). 


252 


THE    DIGESTIVE    ORGANS. 


as  clusters  of  small  lymph-follicles,  similar  to  those  found  in  the 
tongue.  The  pharyngeal  tonsil  presents  numerous  irregularly 
formed  crypts,  lined  by  stratified  pavement  epithelium.  These  crypts 
are  often  widened  at  the  base  and  are  provided  with  irregular  sac- 
cular enlargements.  The  crypts  are  all  surrounded  with  lymphoid 
tissue,  which  may  be  regarded  as  diffuse  lymphoid  tissue  in  which 
are  found  numerous  lymphoid  follicles,  often  showing  germ-centers. 
The  lymphoid  tissue  is  bounded  externally  by  fibrous  tissue,  septa 
of  which   pass  into  the   lymphoid  tissue  surrounding   the  crypts. 


Fig.  196. — Section  through  the  pharyngeal  tonsil  of  man;  X  ^Yz'-  ^gP^  Arcus 
glosso-palatinus  ;  ep,  epithelium ;  ft,  crypt ;  M,  striated  muscle  ;  nl,  lymphoid  nodules ; 
S,  connective  tissue  septa ;  st,  remains  of  tonsillar  sinus. 

The  epithelium  lining  the  crypts  or  cavities  of  the  tonsils  shows, 
as  in  the  lingual  follicles,  extensive  degenerative  changes,  resulting 
mainly  in  the  formation  of  variously  shaped  communicating  spaces 
filled  with  lymphocytes  and  leucocytes.      (See  Fig.  ip/-) 

Besides  the  nerves  terminating  in  the  taste-buds,  the  tongue  is 
richly  supplied  with  sensory  nerves  which  terminate  in  free  sen- 
sory endings,  which  may  be  traced  into  the  epithelium,  and  which 
are  especially  numerous  in  the  fungiform  and  circumvallate  papillae  ; 
or  in  smaller  or  larger  end-bulbs  of  Krause  found  in  the  mucosa  of 


THE    ORAL    CAVITY. 


253 


the  fungiform  papillae, 
in  motor  endings. 


The  motor  nerves  of  the  tongue  terminate 


GLANDS  OF  THE  ORAL  CAVITY. 

The  glands  of  the  oral  cavity  comprise  numerous  branched 
tubulo-alveolar  glands  situated  in  the  mucosa  and  submucosa  of 
the  lips,  cheek,  and  tongue;  branched  tubular  glands  in  the  region 
of  the 'circumvallate  papillae;  of  a  pair  of  compound  branched 
alveolar  glands,  the  parotid;  and  of  two  pairs  of  compound 
branched  tubulo-alveolar  glands,  the  submaxillary  and  sublingual. 
These  are  classified  according  to  their  secretions  into  those  secret- 
incr  principally  mucus  (human  sublingual  and  many  of  the  smaller 
oral  glands),  and  known  as  mucous  glands  ;  those  secreting  a  fluid 
albuminoid  substance  containing  no  mucus,  the  serous  glands 
(parotid  glands  and  the  small  glands  near  the  circumvallate  papillae) ; 


Fig    i97._The  area  designated  by  a  in  the  previous  illustration,  shown  by  a  higher 

magnification;    X  about   150:  «,   Leucocytes  in  the  epithelium;  b  one  of  the  spaces 

in  the  epithelium  filled  with  leucocytes  and  more  or  less  changed  epithelial  cells  ;  c, 
blood-vessel ;  d,  normal  epithelium  ;  e,  basal  cell  of  the  same. 

and  those  having  a  mixed  secretion,  mucous  and  serous  glands 
(human  submaxillary).  The  ducts  of  all  these  glands  open  into 
the  cavity  of  the  mouth.  The  ducts  of  the  smaller  oral  glands  are, 
as  a  rule,  short  and  pass  up  through  the  mucosa  and  the  epithelium 
to  open  on  the  free  surface.  The  principal  excretory  ducts  of  the 
large  salivary  glands  are  Steno's  ducts  (Stenson's  ducts),  passing 
from  the  parotid  glands  to  the  mouth  ;  Wharton's  ducts,  the  ducts 
of  the  submaxillary  glands,  and  Bartholin's  ducts  for  the  sublingual 
glands.  The  salivary  glands  consist  of  numerous  lobules  and 
small  lobes  of  ■  glandular  tissue,  surrounded  by  a  thin  fibrous- 
tissue  capsule  which  sends  septa  and  trabeculae  between  the  lobules 
and  lobes.  The  duct  of  each  gland  on  reaching  the  gland  divides 
into  smaller  ducts,  which  penetrate  the  gland  between  the  lobes  and 
lobules,    dividing    and    redividing    in    their    course;    the    terminal 


254  THE    DIGESTIVE    ORGANS. 

branches  enter  the  lobules  and  join  the  tubules  and  alveoli.  The 
ducts  of  the  human  submaxillary  glands  have  been  carefully  inves- 
tigated by  Flint ;  his  account  is  here  followed.  The  submaxillary 
duct  (Wharton's  duct)  generally  divides  into  three  primary  ducts, 
which  extend  in  various  directions  and  are  usually  relatively  short, 
dividing  into  the  interlobular  ducts,  which  often  run  for  relatively 
long  distances  before  giving  off  individual  branches.  They  run  in 
the  connective  tissue  between  the  lobules,  and  give  off  branches 
and  end  in  ducts  which  ramify  between  the  lobules  and  are  known 
as  sublobidar  ducts,  which  in  turn  give  rise  to  lobar  ducts,  which 
generally  ramify  through  three  or  four  divisions  which  follow  in 
close  succession,  forming  the  intralobular  diicts.  These  radiate 
from  the  centre  toward  the  periphery  of  the  lobules,  without,  how- 
ever, reaching  the  periphery.  The  terminal  branches  of  the  intra- 
lobular ducts  are  the  intermediate  ducts  (intercalary),  which  are  in 
communication  with  the  secretory  compartment,  the  tubules. 

The  epithelium  lining  the  different  portions  of  the  large  excre- 
tory ducts  varies  somewhat.  For  a  short  distance  from  their  oral 
end  they  are  lined  by  a  stratified  columnar  epithelium  consisting 
of  two  layers  of  cells  (Wharton's  ducts  are  now  and  then  lined 
for  a  short  distance  by  a  stratified  pavement  epithelium  continuous 
with  that  lining  the  mouth).  Beyond  this  stratified  columnar  epi- 
thelium, which  extends  for  a  variable  distance  along  the  large 
excretory  ducts,  the  interlobular  ducts  and  the  sublobular  ducts  are 
lined  by  a  pseudostratified  columnar  epithelium,  possessing  two 
rows  of  nuclei  (Steiner).  The  intralobular  ducts  are  lined  by  a 
single  layer  of  columnar  cells,  the  basal  half  of  each  cell  showing 
a  distinct  striation.  The  intermediate  portions  of  the  ducts  are 
lined  by  a  low,  cubic,  or  flattened  epithelium.  The  epithelium  of 
the  ducts  rests  on  a  basement  membrane,  consisting  of  very  fine, 
closely  woven  connective-tissue  fibrils  (Flint).  External  to  this 
there  is  a  sheath  of  areolar  connective  tissue,  which  shows  external 
to  the  basement  membrane  a  layer  of  closely  woven  elastic  fibers. 
The  larger  divisions  of  the  duct  have  nonstriated  muscle-cells  in 
their  walls. 

Between  the  membrana  propria  and  the  secreting  epithelium  of 
the  tube,  and  more  especially  in  the  acini,  are  branched  cells  which 
anastomose  with  each  other,  the  so-called  basket  cells.  The  origin 
of  these  cells  has  not  been  fully  determined ;  their  existence  even 
has  been  questioned.  Their  processes  penetrate  between  the  glan- 
dular cells  and  form  a  supporting  structure  for  them.  The  mem- 
brana propria  surrounding  the  entire  glandular  tube  is  in  close 
relationship  to  these  cells. 

We  shall  now  consider  more  in  detail  the  structure  of  the 
alveoli,  tubules,  and  of  the  salivary  glands. 


SALIVARY    GLANDS. 


255 


SALIVARY  GLANDS. 
The  Parotid  Gland  (Serous  Gland). — The  parotid  glands  may- 
be classed  as  compound  branched  alveolar  glands.  The  gland  is 
made  up  of  distinct  lobes  and  lobules.  The  secreting  compart- 
ments consist  of  irregular,  convoluted  tubules,  which  are  joined  by 
a  narrow  intermediate  duct  to  the  intralobular  ducts.  The  epithe- 
lial cells  hning  the  acini  of  this  gland  are  short,  irregularly  colum- 
nar or  cubic  cells,  with  round  or  oval  nuclei,  situated  nearer  the 
basal    portions    of   the    cells,  the  protoplasm    presenting  different 


_- Acini. 


Fig.  198. — Section  through  salivary  gland  of  rabbit,  with  injected  blood-vessels  ;  X  70- 


appearances  according  to  their  physiologic  condition.  When  at 
rest,  the  cells  are  filled  with  fine  granules,  which  are  to  be  regarded 
as  consisting  of  a  substance  from  which  the  specific  secretion  is 
formed,  a  substance  known  as  zymogen,  the  granules  being  known 
as  zymogen  granules.  These  granules  are  in  the  paraplasm  of  the 
cells,  from  which,  they  are  probably  developed.  As  secretion  pro- 
ceeds the  outer  portion  of  the  cell  becomes  free  from  granules,  these 
being  used  up  in  the  formation  of  the  secretion  (Langley). 

The   Sublingual   Gland   (Mucous    Gland). — The   subHngual 
glands   are    compound   branched   tubulo-alveolar    glands.      These 


256 


THE    DIGESTIVE    ORGANS. 


glands  may  be  regarded  as  made  up  of  numerous  smaller  glands. 
The  ducts  divide  and  redivide,  as  above  described,  with  this  exception, 
that  the  secreting  compartments  are  not  joined  to  the  intralobular 
ducts,  with  striated  epithelium,  by  means  of  narrow  intermediate 
ducts,  as  these  divisions  of  the  duct  system  are  lacking  in  these 
glands  (Maziarski).  The  general  arrangement  of  the  secreting 
compartments  in  a  small  portion  of  a  sublingual  gland  is  shown  in 
Fig.  199.  The  size  of  the  tubules  and  alveolar  enlargements 
varies.  In  the  tubules  and  alveoli  there  are  two  varieties  of  cells: 
cells  which  form  mucus  and  cells  which  have  a  serous  secretion. 
The  cells  vv'hich  form  mucus,  appear  clear  in  preparations  treated 
after    the    ordinary    methods    used    in  the  laboratories.      In    fresh 


Fig.  199. — Model  of  a  small  portion  of  a  sublingual  gland  of  man;  X  ^40'  ^^^ 
demilunes  of  Heidenhain  are  more  deeply  shaded  (Maziarski,  "Anatomische  Hefte," 
1901). 


preparations  teased  in  serum  or  in  2^  to  5^  sodium  chlorid  solu- 
tion (Langley),  or  when  fixed  and  stained  after  special  methods,  it 
may  be  seen  that  the  secretion  is  first  formed  in  the  form  of  large 
granules,  consisting  of  a  substance  known  as  mucigen,  which 
breaks  down  to  form  the  mucus,  much  as  described  for  mucous  or 
goblet  cells  (see  page  87).  In  preparations  the  cells  of  which  are 
stored  with  mucigen  the  nuclei  are  situated  at  the  periphery  of  the 
tubules  and  alveoli,  near  the  basement  membranes.  The  cells  with 
serous  secretion  are  situated  in  close  apposition  to  the  basement 
membrane;  they  resemble  in  structure  serous  cells,  and  are  found 
either  singly  or  in  groups  of  crescentic  shape.  These  groups  are 
known  as  the  crescents  of  Giamizzi  or  the  demilunes  of  Hetdenhatn. 
The  margins  of  the  individual  cells  composing  the  crescents  are 


SALIVARY    GLANDS. 


257 


often  so  faintly  outlined  that  the  whole  structure  has  the  appearance 
of  a  large  polynuclear  giant  cell. 

The  demilunar  cells  have  been  variously  interpreted  by  different 
observers.  They  have  been  regarded  as  permanent  cells  with  a 
special  secretion,  as  transitional  structures,  and  again  as  cells  des- 
tined to  replace  the  degenerated  mucous  cells.  Stöhr  (87)  be- 
lieves that  the  cells  of  the  acini  are  never  destroyed  in  the  process 


Intermediate 
duct. 


Crescents  of 
Gianuzzi. 


Fig.  200. — From  section  of  human  submaxillary  gland. 

of  mucous  secretion,  and  that  the  crescents  of  Gianuzzi  are  there- 
fore merely  a  complex  of  cells  containing  no  secretion,  which  have 
been  crowded  to  the  wall  by  the  adjacent  enlarged  and  distended 
cells.  Solger  (96),  on  the  other  hand,  does  not  regard  the  demi- 
lunes as  transitional  structures  whose  function  is  to  replace  the 
destroyed  cells,  but  considers  them  to  be  permanent  secreting  cells 
— an  opinion  which  he  bases  on  the  results  of  special  methods  of 


Connective 
tissue. 


Gland    cell 
of  acinus. 


Intralobu- 
lar duct. 


Intermedi- 
ate duct. 


Fig.  201. — Section  from  parotid  gland  of  man. 

investigation.  According  to  him,  then,  the  mucous  salivary  glands 
are  mixed  glands,  in  that  the  demilunes  consist  of  cells  of  a  serous 
type,  while  the  remaining  elements  are  mucous  in  character.  The 
destruction  of  mucous  cells  during  secretion  is  not  admitted  by  him 
(compare  also  R.  Krause).  This  latter  view  seems  more  in  accord 
v/ith  recent  observations. 
17 


258 


THE    DIGESTIVE    ORGANS. 


The  Submaxillary  Gland  (Mixed  Gland). — The  submaxillary 
gland  of  man  is  a  gland  composed  of  tubules  similar  in  shape  and 
structure  to  those  found  in  the  parotid  gland,  having  a  serous  secre- 
tion, and  of  tubules  with  alveolar  enlargements,  lined  with    cells 


Fig.  202. — Portion  of  a  model  of  a  salivary  gland  with  mucous  secretion  :  a,  intralo- 
bular duct  ;  b,  intermediate  duct  ;  c,  tubules  and  alveoli  lined  by  mucous  cells  ;  d,  demi- 
lunes of  Heidenhain  (from  Böhm  and  Davidoff,  third  German  edition). 

which  form  mucus.  These  mucus-secreting  tubules  are  joined  to 
intermediary  ducts  which  are  branches  of  intralobular  ducts  with 
striated  epithelium.  The  mucus-forming  tubules  show  the  demi- 
lunes of  Heidenhain.     The  submaxillary  glands  of  man  are  there- 


Fig.  203. — A  number  of  alveoli  from  the  submaxillary  gland  of  dog,  stained  in  chrome 
silver,  showing  some  of  the  fine  intercellular  tubules. 


fore  mixed  glands,  with  both  serous  and  mucous  secretion,  the  re- 
spective tubules  or  groups  of  tubules  showing  the  characteristics  of 
mucous  and  serous  glands.  In  Fig.  202  is  shown  a  portion  of  a 
model  of  a  salivary  gland,  with  mucous  secretion. 


SALIVARY    GLANDS.  259 

By  means  of  various  methods  the  existence  of  a  network  of 
tubules  surrounding  the  glandular  cells  may  be  demonstrated  both 
in  the  serous  and  mucous  glands.  The  same  arrangement  may  be 
observed  in  the  case  of  the  cells  forming  the  demilunes.  The 
course  of  these  tubules  may  be  followed  to  their  junction  with  the 
lumen  of  the  secreting  portion  of  the  gland  tubule,  and  the  whole 
structure  would  seem  to  indicate  that  the  entire  surface  of  the  cells 
is  concerned  in  the  act  of  secretion  (Erik  Müller,  95  ;  Stöhr, 
96,  11). 

As  to  the  part  that  the  intermediate  tubules  and  the  intralobular 
tubes  play  in  the  process  of  secretion,  Merkel's  (83)  theory  is  of 
interest.  He  believes  that  the  former  yield  a  part  of  the  water  in 
the  saliva,  while  the  salts  are  furnished  by  the  rod-shaped  epithe- 
lium of  the  intralobular  tubes.  These  views  of  Merkel  have  been 
questioned,  as  it  has  been  shown  by  chemic  analysis  that  the 
relative  quantity  of  water  and  salts  in  the  secretion  of  the  salivary 
glands  is  not  at  all  proportionate  to  the  number  of  the  intermediate 
tubules  and  intralobular  tubes.  For  example,  Werther  finds  that 
although  a  great  many  intermediate  tubules  are  present  in  the  par- 
otid gland  of  the  rabbit  and  none  at  all  in  the  submaxillary  gland 
of  the  dog,  nevertheless  the  secretions  of  these  glands  contain  equal 
quantities  of  water.  Furthermore,  the  secretions  of  the  parotid  of 
the  rabbit  and  of  the  sublingual  of  the  dog  show  equal  quantities  of 
salts,  in  spite  of  the  fact  that  in  the  former  there  are  large  numbers 
of  intralobular  tubes  with  rod-shaped  epithelium  and  in  the  latter 
none  at  all. 

THE  SMALL  GLANDS  OF  THE  MOUTH. 

Besides  the  larger  glands,  there  are  in  the  oral  cavity  numerous 
small  lobular,  tubulo-alveolar  and  simple  branched  tubulo-alveolar 
■glands.  They  are  mostly  glands  with  mucous  secretion.  In 
many  of  them  demilunes  of  Heidenhain  may  be  made  out,  most 
clearly  in  those  of  the  lips  (J.  Nadler).  They  are  known,  accord- 
ing to  their  location,  as  glandulae  labiales,  palatinse,  and  linguales. 
The  absence  of  intralobular  tubes  and  well-defined  intermediate 
tubules  is  characteristic  of  all  the  smaller  glands  of  the  oral  cavity. 
As  a  consequence  the  secreting  tubules  are  composed  almost 
entirely  of  those  parts  corresponding  to  the  acini  of  the  larger 
glands.  Branched  tubular  glands,  with  serous  secretion,  known 
as  v.  Ebner's  glands,  occur  in  the  tongue,  their  ducts  opening  into 
the  depressions,  of  the  circumvallate  and  foliate  papillae,  while  the 
secreting  tubules  extend  into  the  muscular  portion  of  the  tongue. 
The  general  character  of  v.  Ebner's  glands  is  shown  in  Fig.  204. 

The  salivary  glands  and  smaller  glands  of  the  mouth  have  a 
rich  blood  supply.  In  the  salivary  glands  the  arteries  follow  the 
ducts  through  their  repeated  branching,  ultimately  ending  in  capil- 
laries which  form  a  network  inclosing  the  acini  and  the  terminal 


26o 


THE    DIGESTIVE    ORGANS. 


portions  of  the  system  of  ducts.  The  blood-vessels  for  each  lobule 
are  quite  distinct,  forming  only  _  few  anastomoses  with  those  of 
neighboring  lobules. 

The  Lymphatics. — In  the  connective  tissue  surrounding  and 
separating  the  acini  there  are  found  clefts,  which  contain  lymph. 
These  clefts  are  in  part  between  the  blood-capillaries  and  the  base- 
ment membranes.  Lymph-vessels  are  found  in  the  connective  tissue 
separating  the  lobules  and  lobes  of  the  gland,  in  which  they  follow 
the  duct  system.  Lymph-vessels  have  not  been  found  in  the 
lobules. 


Fig.    204. — Model  of   a  gland    of  v.    Ebner,  from  a  boy  fourteen   years  old  ;    X  ^70- 
(Maziarski,  "Anatomische  Hefte,"  1901.) 


The  nerve  supply  of  the  salivary  glands,  may,  owing  to  the  im- 
portance of  these  structures,  receive  somewhat  fuller  consideration. 
Their  nerve  supply  is  from  several  sources.  That  of  the  sublin- 
gual and  submaxillary  glands  will  be  considered  first.  Sensory 
nerve-fibers  (no  doubt  the  dendrites  of  sensory  neurones,  the  cell- 
bodies  of  which  are  situated  in  the  geniculate  ganglion)  terminate  in 
free  sensory  endings  in  the  large  excretory  ducts  and  their  branches. 
These  meduUated  fibers  accompany  the  ducts  in  the  form  of  small 
bundles.  From  place  to  place  one  or  several  fibers  leave  these 
bundles  and,  after  dividing  a  number  of  times,  lose  their  medullary 
sheaths.  After  further  division  the  nonmedullated  branches  form 
plexuses  under  the  epithelial  lining  of  the  ducts.  From  the  fibers 
of  these  plexuses  terminal  fibrils  are  given  off,  which  enter  the 
epithelium,  to  end,  often  near  the  free  surface,  on  the  epithelial  cells 
(Arnstein,  95;  Huber,  96).     The  secretory  cells  of  the  acini  receive 


SALIVARY    GLANDS.  201 

their  innervation  from  sympathetic  neurones.  The  cell-bodies  of 
those  supplying  the  sublingual  glands  are  grouped  in  a  number  of 
small,  s}'mpathctic  ganglia  situated  in  a  small  triangle  formed  by  the 
lingual  nerve,  the  chorda  tympani  and  Wharton's  duct,  the  chorda- 
lingual  triangle.  These  ganglia  may  be  known  as  the  sublingual 
ganglia  (Langle\').  The  cell-bodies  of  the  sympathetic  neurones 
supplying  the  secretory  cells  of  the  submaxillary  glands  are  grouped 
in  small  ganglia  situated  on  Wharton's  duct  just  before  it  enters  the 
gland,  in  the  hilum  of  the  gland,  and  on  the  interlobar  and  inter- 
lobular ducts  ;  they  may  be  spoken  of  collectively  as  the  submax- 
illary ganglia.  In  the  glands  under  discussion,  the  neuraxes  of  the 
sympathetic  neurones  are  grouped  to  form  small  bundles,  which 
divide  repeatedly,  the  resulting  divisions  joining  to  form  plexuses 
situated  in  the  outer  portion  of  the  walls  of  the  ducts,  and  as  such 
may  be  followed  along  the  ducts,  the  bundles  of  nerve-fibers  be- 
coming smaller  and  the  division  of  the  bundles  of  fibers  and  the 
individual  fibers  occurring  oftener  as  the  smaller  divisions  of  the 
system  of  ducts  are  reached.  On  reaching  the  acini,  the  termiinal 
branches  of  the  nerve -fibers  form  a  plexus  outside  of  the  basement 
membrane,  epilamellar  plexjis  ;  from  this  branches  are  given  off 
which  penetrate  the  basement  membrane,  some  forming  dihypolam- 
ellar plexus,  others  ending  on  the  gland-cells  in  small  granules  or 
clusters  of  granules  (Arnstein).  Throughout  their  entire  course  the 
neuraxes  of  the  sympathetic  neurones  are  varicose,  nonmedullated 
nerve-fibers.  The  nerve-fibers  of  the  chorda  tympani  end  in  ter- 
minal end-baskets,  inclosing  the  cell-bodies  of  the  sympathetic 
neurones  found  in  the  sublingual  and  submaxillary  ganglia,  and  not 
in  the  glands,  as  generally  stated  by  writers.  The  increase  of  secre- 
tion from  the  submaxillary  and  sublingual  glands  on  direct  or  indi- 
rect stimulation  of  the  chorda  tympani  is  due,  therefore,  not  to  a 
direct  stimulation  of  the  gland-cells  by  the  fibers  of  this  nerve,  but 
to  a  stimulation  of  the  sympathetic  neurones  of  the  sublingual  and. 
submaxillary  ganglia,  the  neuraxes  of  which  convey  the  impulse  to 
the  gland-cells.  These  glands  have  a  further  nerve  supply  from  the 
superior  cervical  ganglia  of  the  cervical  sympathetic.  The  neuraxes 
of  sympathetic  neurones,  the  cell-bodies  of  which  are  situated  in  the 
superior  cervical  ganglia,  accompany  the  blood-vessels  to  the  sub- 
lingual and  submaxillary  glands  ;  their  mode  of  termination  is, 
however,  not  as  yet  determined.  The  cell-bodies  of  the  sympathetic 
neurones  here  in  question  are  surrounded  by  end-baskets  of  nerves 
which  leave  the  spinal  cord  through  the  second,  third,  and  fourth 
dorsal  spinal  roots.  The  blood-vessels  of  the  salivary  glands  are 
also  richly  supplied  with  vasomotor  nerves,  the  neuraxes  of  sympa- 
thetic neurones,  which  terminate  on  the  muscle-cells  of  their  walls. 
The  nerve  supply  of  the  parotid  glands  is,  in  the  main,  like  that  of 
the  other  salivary  glands  here  described,  although  it  has  not  been 
worked  out  with  the  same  detail.  The  cell-bodies  of  the  sympathetic 
neurones,  the  neuraxes  of  which  innervate  the  gland-cells,  are,  it 


202  THE    DIGESTIVE    ORGANS. 

would  appear,  situated  in  the  otic  ganglia.  The  nerve-ending  in 
the  smaller  glands  of  the  mouth  is  similar  to  that  given  for  the 
salivary  glands,  as  has  been  shown  by  Retzius  and  other  observers. 
It  is  very  probable  that  the  cell-bodies  of  the  sympathetic  neu- 
rones, the  neuraxes  of  which  innervate  the  glands  of  the  tongue,  are 
situated  in  the  small  sympathetic  ganglia  found  on  the  lingual 
branches  of  the  glossopharyngeal  and  lingual  nerves. 


B,  THE  PHARYNX  AND  ESOPHAGUS. 

Pharynx. — The  epithelium  of  the  pharynx  is  of  the  stratified 
squamous  variety,  and  also  contains  prickle  cells  and  keratohyalin. 
(See  Skin.)  A  stratified  ciliated  epithelium  is  present  only  in  the 
fornix  in  the  region  of  the  posterior  nares.  The  area  covered  by 
this  type  of  epithelium  is  more  extensive  in  the  fetus  and  new-born, 
and  extends  over  the  whole  nasopharyngeal  vault.  In  the  human 
embryo  the  superficial  epithelial  cells  of  the  esophagus  possess  cilia 
up  to  the  thirty-second  week  (Neumann,  76).  The  papillae  of  the 
mucosa  are  loosely  arranged  and  are  in  the  form  of  slender  cones. 
The  mucosa  of  the  pharynx  contains  diffuse  adenoid  tissue  rich  in 
cells  which  in  some  places  forms  accessory  tonsils  {z'id.  p.  251); 
it  is  bounded  externally  by  a  well -developed  layer  of  elastic  fibers 
which  occupies  the  same  relative  position  as  does  the  muscularis 
mucosae  in  the  esophagus.  External  to  this  elastic  layer,  there  is 
found  a  muscular  coat  consisting  of  striated  muscle-fibers. 

Esophagus. — The  esophagus  is  lined  by  a  stratified  pavement 
epithelium,  which  rests  on  a  papillated  mucosa,  consisting  of  fibrous 
tissue  which  contains  {&\sf  elastic  fibers  and  is  bounded  externally 
by  a  muscularis  mucosae,  the  majority  of  the  cells  of  which  show 
a  longitudinal  arrangement.  External  to  the  muscularis  mucosae 
there  is  -found  a  well-developed  submucosa,  consisting  of  loosely 
woven  fibro-elastic  connective  tissue.  Outside  of  the  submucosa 
there  is  found  a  muscular  layer,  consisting  of  an  inner  circular  and 
an  outer  longitudinal  layer.  These  muscular  layers  consist  in  the 
upper  half  of  the  esophagus  mainly  of  striated  muscle-fibers,  while 
in  the  lower  half  they  consist  almost  wholly  of  nonstriated  muscular 
tissue.  There  is,  however,  no  sharply  defined  line  of  demarcation 
between  the  two  types  of  muscular  tissue,  as  the  fibers  of  the 
unstriped  variety  penetrate  for  some  distance  upward  into  the 
substance  of  the  striated  muscle,  giving  the  tissue  here  a  mixed 
character. 

The  esophagus  contains  two  varieties  of  glands:  (i)  Mucous 
glands  of  the  type  of  branched  tubulo-alveolar  glands.  The  secret- 
ing portions  of  these  glands  are  situated  in  the  submucosa,  while 
the  ducts  pass  through  the  muscularis  mucosae  to  the  surface. 
The  secreting  tubules  and  alveoli  are  lined  by  mucous  cells  ;  demi- 
lunes are  absent.      The   ducts,  which   often  show   cystic   dilations. 


THE    PHARYNX    AND    ESOPHAGUS. 


263 


are  lined  for  the  greater  part  by  a  single  layer  of  columnar  cells ; 
at  their  termination  they  often  possess  a  lining  of  stratified  pave- 
ment epithelium.  (2)  The  other  variety  of  glands  are  found  in  two 
zones,  the  one  situated  at  the  upper  end  of  the  esophagus,  in  a 
region  opposite  the  cricoid  cartilage  to  the  fifth  tracheal  cartilage 
(superficial  glands  of  esophagus,  Hewlett;  upper  cardiac  gland, 
Schaffer),  the  other  at  the  end  of  the  esophagus,  just  before  it  enters 
the  stoniach — the  esophageal  cardiac  glands.  These  glands  are 
situated  above  the  muscularis  mucosa,  and  are  of  the  branched 


jr.-»    Epithelium. 

^r^"    Mucosa. 

•    Muscularis 
mucosae. 

i^—   Submucosa. 


—   Circular  layer 
of  muscle. 


--  Longitudinal 
muscle  layer. 


—  Outer  connec- 
tive-tissue 
coat. 


Fig.  205. — Section  of  esophagus  of  dog;  X  ^^• 

tubular  variety.  The  ducts  of  these  glands,  which  reach  the 
surface  through  the  apices  of  the  connective  tissue  papillae,  are 
lined  by  a  single  layer  of  columnar  epithelial  cells.  The  secretmg 
portions  of  the  tubules  are  lined  by  shorter  columnar  cells.  Here 
and  the-e  cells  like  the  parietal  cells  of  the  fundus  glands  of  the 
stomach,  to  be. described  later,  are  also  found,  as  also  cells  showmg 
a  mucous  secretion.  The  cardiac  glands  of  the  esophagus  are 
similar  to  the  glands  of  the  same  name  found  at  the  cardiac  end 
of  the  stomach,  with  which  they  may  be  said  to  be  contmuous,  and 
which  will  receive  further  consideration. 


264  THE    DIGESTIVE    ORGANS. 

C  THE  STOMACH  AND  INTESTINE. 

J.  GENERAL  STRUCTURE  OF  THE  INTESTINAL  MUCOUS 
MEMBRANE. 

The  mucous  membrane  of  the  stomach  and  intestine,  unlike 
that  of  the  esophagus  and  oral  cavity,  possesses  an  epithelium  of 
the  simple   columnar  variety  with  elongated  cells  (about  22  /^  in 


Alveolus 
of  gland. 


Mucosa. : 


Basal  epi- 
thelial 
cells. 

Gland- 
cells. 


-    Lumen. 


Branched 
papilla 
of  mu- 
cosa. 


Fig.    206. — Part   of   section   of  human    esophagus,    showing    a    cardiac    gland    with    a 

dilated  duct;  X  ^^o. 


height).  At  the  cardia  the  stratified  squamous  epithelium  of  the 
esophagus  terminates  abruptly,  the  basilar  layer  of  the  esophageal 
epithelium  being  continued  as  the  simple  columnar  epithelium  of 
the  stomach.  In  the  intestine  the  epithelium  shows  a  well-marked 
striated  cuticular  border,  striated  protoplasm  in  the  outer  ends  of 
the  cells,  extending  to  the  immediate  vicinity  of  the  nuclei,  which 


THE    STOMACH    AND    INTESTINE.  265 

are  situated  in  the  basal  portions  of  the  cells.  The  basal  portion  of 
each  cell  consists  of  nonstriated  protoplasm,  ending  in  a  longer  or 
shorter  process  which  extends  to  the  basement  membrane,  or  possibly 
even  penetrates  it.  The  epithelial  cells  have  the  power  of  produc- 
ing mucus,  a  phenomenon  which,  in  the  normal  condition,  rarely 
embraces  whole  areas  of  epithelium  ;  these  cells  (goblet  cells)  are 
usually  surrounded  by  others  which  are  unchanged  (for  details  about 
goblet  cells  see  General  Histology,  p.  87).  Throughout  the  entire 
intestinal  tract  the  epithelium  forms  simple,  branched,  and  compound 
tubular  and  alveolar  glands.  These  are  depressions  lying  in  the 
mucosa,  and  only  in  the  duodenum  extend  beyond  it  into  the  sub- 
mucosa. 

The  mucosa  consists  of  adenoid  tissue,  consisting  of  reticular 
fibers  and  a  fine  network  of  elastic  fibers,  containing  relatively  few 
cells.  It  fills  the  interstices  between  the  glands,  and  often  forms  a 
thin  but  continuous  layer  (granular  layer  of  F.  P.  Mall)  below  the 
glands.  It  is  therefore  obvious  that  the  development  of  the 
mucosa  is  inversely  proportionate  to  the  number  and  the  density  of 
arrangement  of  the  glands  ;  when  the  latter  are  present  in  large 
numbers,  as,  for  instance,  in  the  stomach,  the  mucosa  is  reduced  to 
a  minimum.  In  the  small  intestine  it  forms  not  only  the  perma- 
nent folds,  but  also  certain  leaf-like  and  finger-like  'elevations 
known  as  villi,  which  are  covered  with  epithelium  and  project  into 
the  lumen  of  the  intestine,  thus  increasing  to  a  considerable  extent 
the  surface  area  of  the  mucous  membrane.  In  the  mucosa  are 
found  small  nodules  of  adenoid  tissue.  These  are  spoken  of  as 
lenticular  glands  when  occurring  in  the  stomach,  as  solitary  glands 
when  found  in  the  upper  portion  of  the  small  intestine  and  in  the 
large  intestine.  In  the  lower  portion  of  the  small  intestine  they  are 
grouped  to  form  the  agminated  glands,  or  Peyer's  patches,  which, 
when  large,  extend  into  the  submucosa.  In  the  external  portion 
of  the  rtiucosa  there  is  found  a  thin,  somewhat  denser  layer,  known 
as  the  stratum  fibrosum  (F.  P.  Mall),  consisting  mainly  of  white 
fibrous  tissue  (Spalteholz) ;  and  external  to  this  is  a  layer  consisting 
of  two  or  three  strata  of  unstriped  muscle-fibers,  the  umscularis 
miicoscB.  As  a  rule,  it  is  composed  of  an  inner  circular  and  an 
outer  longitudinal  layer.  This  arrangement  is  interrupted  only 
where  the  larger  glands  and  follicles  penetrate  into  the  submucosa. 
The  epithelium  with  the  glands,  the  mucosa  with  its  lymph-nodules, 
and  the  muscularis  mucosae  form  together  the  mucous  membrane, 
or  tunica  mucosa. 

Below  the  mucous  membrane  is  the  connective-tissue  sjibmucosa. 
This  is  characterized  by  its  loose  structure,  and  consequently  affords 
considerable  mobility  to  the  mucous  membrane.  In  the  small  intes- 
tine it  forms  a  large  number  of  permanent  transverse  folds  known 
as  vahndcz  conniventcs  (Kerkring).  In  the  submucosa  of  the 
duodenum  occur  the  secreting  portions  oi  Brunn cr' s  glands  (gland- 
ulae  duodenales),  and  in  the  small  intestine  the  larger  h^mph-nodes 
and  Peyer's  patches. 


266 


THE    DIGESTIVE    ORGANS. 


External  to  the  submucosa  is  the  muscular  coat,  which  generally 
consists  of  two  layers  of  unstriped  muscle-tissue.  The  inner  layer 
is  composed  of  circular  fibers  (stratum  circulare)  ;  the  outer  layer,  of 
longitudinal  fibers  (stratum  longitudinale).  In  the  colon  the  longi- 
tudinal layer  forms  definite  bands,  the  tceiiice  coli.  In  some  regions 
the  circular  fibers  are  also  considerably  reinforced,  particularly  in 
the  plic(2  sigmoidecB  which  lie  between  the  taeniae  coli.  At  these 
points  the  longitudinal  layer  also  is  thickened.  In  the  rectum  the 
circular  fibers  form  the  internal  sphincter  ani  muscle.  In  the 
stomach  a  third  layer  is  added  to  the  two  already  mentioned,  with 
fibers  running  obliquely.  It  lies  internal  to  the  circular  fibers,  but 
does  not  form  a  continuous  layer. 

According  to  Legge,  elastic  fibers  are  present  throughout  the 
entire  digestive  tract  of  all  adult  mammalia  and  vary  only  in  minor 
details  in  the  different  species.  In  regions  in  which  the  tunica  mus- 
cularis  is  prominent  the  elastic  fibers  attain  a  considerable  size. 
There  is  also  a  difference  in  their  development  in  Carnivora  and 
herbivora.  In  general,  they  form  a  dense  network,  present  not  only 
in  the  serous  layer,  but  also  in  the  submucosa  and  mucosa.  These 
fibers  preserve  the  elasticity  of  the  intestinal  walls  and  resist  any 
hyperextension  of  the  glands  and  follicles. 

The  intestine  is  covered  externally  by  the  peritoneum,  forming 
the  serous  coat,  which  consists  of  an  inner,  very  thin  connective - 
tissue  layer  (subserosa)  and  an  outer  layer  of  mesothelial  cells. 


2.  THE  STOMACH. 

The  general  structure  of  the  gastric  mucous  membrane  is  essen- 
tially the  same  as  that  of  the   intestinal   canal.      It  consists  of  a 

relatively  coarse  adenoid  reticu- 
lum, the  spaces  of  which  contain 
lymphocytes  and  leucocytes,  and 
plasma  cells.  Thin  strands  or 
bundles  of  nonstriated  muscle 
cells  may  be  traced  from  the 
muscularis  mucosae  to  various 
levels  in  the  mucosa.  It  pre- 
sents depressions  or  infoldings 
known  as  crypts  (foveolae,  stom- 
ach-pits, gland  ducts)  into  which 
the  glands  open.  In  the  fundus 
the  crypts  attain  a  depth  of  from 
one-fifth  to  one-sixth  the  thick- 
ness of  the  mucous  membrane. 
In  the  pylorus  they  are  deeper, 
many  of  them  here  extending 
through  half  the  mucous  membrane  and  some  even  reaching  to 
near  the  muscularis  mucosae.     The  epithelium  of  the  crypts  and 


Fig.  207  — Epithelium  of  human  stom- 
ach, covenng  the  fold  of  mucosa  between 
two  gastric  crypts  ;   X  70O- 


THE   STOMACH    AND    INTESTINE. 


267 


that  of  the  folds  between  them  is  composed  of  long,  slender  cells, 
with  basally  situated  nuclei.  That  portion  of  the  cell-body  near 
its  free  margin  contains  very  little  protoplasm,  but  presents  a  well- 
developed  mucous  .plug  or  theca,  occupying  the  outer  one-fourth  or 
one-third  of  the  cell ;  the  region  of  the  cell  containing  the  nucleus 
possesses  more  protoplasm.  This  part  of  the  cell  extends  down- 
ward  in   a   curved  process   of  diminishing   size,  which   assumes  a 

position  parallel  to  the  cor- 
responding parts  of  the 
neighboring  cells,  and 
nearly  parallel  to  the  base- 
ment membrane. 

Three  varieties  of 
glands  occur  in  the  stom- 
ach :  (i)  Cardiac  glands; 
(2)  fundus  glands  ;  (3)  py- 
loric glands. 

►  Bodies  of  gas- 
tric glands. 


►  Gastric  crypts 

and  necks 

of  glands. 


►  Fundus. 


-^>----  Mucosa. 


Fig.  208. — From  vertical  section  through 
fundus  of  human  stomach  ;  y^^  60:  a  and  d,  Inter- 
lacing fibers  of  the  muscularis  mucosae  ;  from  a 
and  i  muscular  fibers  enter  the  mucosa.  The 
fibers  of  the  layer  i  penetrate  those  of  layer  a. 


Fig.  209. — A  number  of  fundus 
glands  from  the  fundus  of  the  stom- 
ach of  young  dog,  stained  after  the 
chrome-silver  method,  showing  the 
system  of  fine  canals  surrounding 
the  parietal  cells  and  communicat- 
ing with  the  lumen  of  the  glands. 


I.  The  cardiac  glands  have  recently  been  subjected  to  careful 
investigation  by  Bensley ;  his  account  is  here  followed.  They 
occur  in  the  region  of  the  junction  of  the  esophagus  and  stomach, 
occupying  a  zone  varying  somewhat  in  width,  but  may  be  as  w^ide 
as  4.3  cm.  The  glands  are  of  the  type  of  branched  tubulo-alveolar 
glands.  The  tubules  and  alveoli  are  not  of  uniform  structure. 
The   majority  of   the  lining   cells   are   mucus    secreting  cells,  and 


268 


THE    DIGESTIVE    ORGANS. 


may  be  recognized  as  such  in  suitably  stained  preparations,  cells 
with  zymogen  granules,  similar  to  the  chief  cells  of  the  body  of  the 
fundus  glands  (see  these),  are  also  found,  as  also  the  parietal  cells, 
as  found  in  the  latter  glands.  The  cardiac  glands  may  be  regarded 
as  decadent  structures. 

2.  The  fundus  gla7ids  (peptic  glands)  consist  of  a  crypt  or 
foveola,  into  which  empty  three  to  five,  or  even  more,  unbranched 
and  branched  tubules,  which  often  show  irregular  terminal  enlarge- 


Epithelium  of 
esophagus. 


"    Cardiac  gland. 


Junction  of 
esophagus 
and  stomach. 

Epithelium  of 
stomach. 


Gastric  crypt. 


Fig.  2IO. — From  a  section  through  the  junction  of  the  human  esophagus  and  cardia  ; 

X50. 


ments.  The  tubules  vary  in  length,  measuring  from  0.4  to  2.2 
mm.  The  upper  end  of  a  fundus  tubule  is  slightly  narrower  and 
presents  structural  peculiarities,  and  is  known  as  the  neck  of  the 
gland.  The  main  portion  of  the  gland  is  called  its  body,  and  the 
region  at  its  distal  blind  end  the  fundtis. 

The  fundus  glands,  as  their  name  suggests,  are  found  in  the  fundus 
or  cardiac  end  of  the  stomach,  and  are  lined  by  two  kinds  of  cells  : 
parietal  (border  cells,  acid,  oxyntic,  or  delomorphous  cells — R. 
Heidenhain,  69 ;   Rollet,  70)  and  chief,  central,  peptic,  or  adelomor- 


THE    STOMACH    AND    INTESTINE.  269 

phous  cells.  The  parietal  cells  lie  against  the  walls  of  the  gland — that 
is,  they  rest  on  its  basement  membrane — and  are  particularly  numer- 
ous in  the  neck  and  body  of  the  gland,  but  not  so  numerous  in  its  fun- 
dus. Their  bodies  often  extend  more  or  less  beyond  the  even  line 
of  the  remaining  cells,  thus  forming,  together  with  the  membrana 
propria,  a  protuberance  (particularly  noticeable  in  the  pig,  where 
almost  the  entire  cell  may  be  enveloped  by  the  basement  membrane, 
giving  it  an  appearance  of  being  entirely  extraglandular).  Toward 
the  lumen  of  the  gland  the  contour  of  these  cells  is  modified  by 
pressure  on  the  part  of  the  adjacent  cells  belonging  to  the  other 
variety,  and  they  are  indented  according  to  the  number  of  the  latter. 
Occasionally,  a  process  is  seen  extending  from  a  parietal  cell  to  the 
lumen  of  the  gland.  The  parietal  cells  are  larger  than  the  cells  of 
the  other  variety  and  richer  in  protoplasm  ;  they  are  of  an  irregular 
oval  or  triangular  shape  and  possess,  as  a  rule,  a  single  nucleus, 
although  in  man  numerous  parietal  cells  with  two  nuclei  are  found. 
The  parietal  cells  are  clearer  in  fresh  preparations  than  are  the  chief 
cells,  while  in  fixed  preparations  the  reverse  is  generally  the  case. 
They  stain  deeply  in  Heidenhain's  iron-lac-hematoxylin,  are  dark- 
ened by  osmic  acid,  and  show  an  affinity  for  acid  stains,  especially 
for  eosin,  also  for  congo-red  and  for  neutral  carmine  solutions. 

According  to  Erik  Müller  and  Golgi  (93),  there  exists  in  the 
peripheral  protoplasm  of  each  parietal  cell  a  system  of  canals  in 
the  form  of  a  network  communicating  with  the  lumen  of  the  gland 
and  varying  in  structure  according  to  the  physiologic  condition  of 
the  cell — wide-meshed  in  a  state  of  hunger  and  fine-meshed  during 
digestion.  A  peripheral  zone  differing  from  the  rest  of  the  cell- 
body  may  occasionally  be  demonstrated  in  the  parietal  cells  (mouse) 
by  using  the  method  of  von  Altmann. 

The  chief  cells  are  short,  irregular,  columnar  structures  whose 
narrower  portions  point  toward  the  lumen  of  the  gland.  They  are 
situated  either  directly  between  the  lumen  and  the  basement  mem- 
brane of  the  gland,  or  their  basilar  surfaces  .border  on  a  delomor- 
phous  cell.  They  are  found  throughout  the  tubule  of  the  gland 
and  occupy  the  spaces  between  the  delomorphous  cells.  The  chief 
cells  of  the  fundus  glands  are  of  two  varieties,  as  has  been  shown 
by  Bensley.  The  chief  cells  of  the  body  of  the  gland  are  charac- 
terized by  the  possession  of  relatively  large  zymogen  granules, 
which  are  found  in  the  inner  portion  of  the  cells.  These  granules 
are  used  up  during  secretion.  The  outer  or  basal  portion  of  the 
cells  contains  a  prozymogen,  not  in  granular  form  but  recognized  by 
its  staining  reaction.  The  chief  cells  of  the  neck  are  slightly 
smaller  than  those  of  the  body,  and  differ  from  these  in  that  they 
do  not  possess  zymogen  granules  and  prozymogen  only  in  small 
amounts,  but  show  by  their  reaction  to  certain  stains  that  they  are 
mucus-secreting  cells. 

The  structure  of  the  pyloric  region  of  the  stomach  differs  in 
some   respects   from   that  of  the  cardiac  end   and  fundus.     There 


270 


THE    DIGESTIVE    ORGANS. 


is,  however,  no  sharply  defined  boundary  between  fundus  and 
pylorus,  but  a  transitional  zone  in  which  changes  gradually  take 
place.  Toward  the  pylorus  the  gastric  crypts  gradually  become 
deeper  and  the  parietal  cells  decrease  in  number.  Here  also  the 
glands  branch  more  freely.  In  the  pylorus  itself  the  crypts  fre- 
quently extend  half-way  through  the  thickness  of  the  mucous 
membrane,  often  even  penetrating  nearly  to  the  muscularis  mucosae, 
in  which  case  the  corresponding  tubules  become  tortuous  and  arch 
over  the  muscularis  mucosae.  The  glands  of  the  pyloric  region 
are  therefore  to  be  classified  as  branched  tubular  glands  (De  Witt). 


Epithelium  ■ 
of  fold  be- 
tween gas- 
tric crypts. 


Gastric 
crypt. 


Pyloric 
gland. 


Mucosa.  »».'■ 


Muscularis 
mucosae. 


Fig.  211. — From  vertical  section  through  human  pylorus  ;  X  about  60. 


Among  the  branched  pyloric  glands  are  found  glands  which  show 
no  distinct  branching.  The  most  important  feature  is  that  in  the 
great  majority  of  the  tubules  only  a  single  variety  of  cell  is  pres- 
ent in  the  pyloric  gland.  (Only  here  and  there  are  found  parietal 
cells  in  the  pyloric  glands  of  the  human  stomach.)  These  cells 
may  be  compared  with  the  chief  cells  of  the  neck  regions  of  the 
fundus  glands,  in  that  they  show  no  zymogen  granules,  and  prozy- 
mogen  only  in  small  quantity,  and  on  staining  with  special  stains,  it 
can  be  shown  that  their  secretion  is  mucus.  They  are  of  colum- 
nar shape,  and  more  uniformly  so  than  the  chief  cells  of  the  fundus 


THE    STOMACH    AND    INTESTINE. 


271 


glands — a  condition  probably  due  to  the  general  absence  of  delo- 
morphous  cells.  In  the  immediate  vicinity  of  the  gastroduodenal 
valve  the  pyloric  glands  become  shorter,  and  other  glands,  which 
extend  into  the  submucosa,  and  which  are  identical  in  structure 
with  the  glands  of  Brunner  in  the  duodenum,  make  their  appear- 
ance. In  this  portion  of  the  pylorus  are  also  a  few  scattered  villi, 
which  from  their  structure  may  be  considered  as  belonging  to  the 
duodenum  {vid.  Fig.  218). 

In  the  normal  condition  the  mucosa  of  the  stomach  contains 
solitary  lymph-nodules  (lenticular  glands)  in  the  fundus  region ; 
they  are,  however,  more  frequent  in  the  pyloric  region ;  well-defined 
lymph-nodules  are  constantly  present  in  the  immediate  vicinity 
of  the  pylorus. 

The  muscularis  mucosae  is  usually  composed  of  three  layers, 
the  fibers  of  the  individual  layers  forming  distinct  interlacing  bun- 
dles. Individual  muscle-fibers  very  frequently  branch  off  from  the 
inner  layer,  assume  a  vertical  position  and  disappear  among  the 
glands.  This  arrangement  is  especially  well  seen  in  the  muscularis 
mucosae  of  the  fundus  of  the  stomach  (Fig.  208). 

Only  the  inner  and  middle  layers  of  the  muscular  coat  of  the 
stomach  enter  into  the 
formation  of  the  sphinc- 
ter pylori  (Fig.  218). 
The  fibers  of  the  outer 
layer,  however,  pene- 
trate through  the  sphinc- 
ter pylori  and  may  even 
be  traced  into  the  sub- 
mucosa. When  these 
alone  contract,  the  mus- 
cular bundles  of  the 
sphincter  act  somewhat 
as  pulleys,  and  a  mod- 
erate dilatation  of  the 
lumen  of  the  pylorus 
is  the  result  ( dilatator 
pylori,  Rüdinger,  97 ). 
(For  further  particulars  about  the  stomach,  compare  Oppel,  96.) 

The  changes  which  the  epithelium  and  the  secretory  cells  of  the 
stomach  undergo  during  secretion  are  of  special  importance.  These 
relations  have  been  carefully  studied  in  animals  by  R.  Heidenhain 
(83),  As  far  as  our  present  knowledge  goes,  it  would  seem  that  the 
same  processes  also  occur  in  man.  In  a  state  of  hunger  the  chief 
cells  of  the  fundus  are  large  and  contain  numerous  zymogen  gran- 
ules, while  the  parietal  cells  are  small ;  in  certain  cases  the  parietal 
cells  abandon  their  mural  position  and,  like  the  chief  cells,  border 
upon  the  lumen  of  the  gland.  During  the  first  few  hours  of  diges- 
tion the  chief  cells  remain  large,  while  the  parietal  cells  increase  in 


Mucosa. 


Fig.  212. — From  section  through  human  pylorus; 
X600. 


2/2 


THE    DIGESTIVE    ORGANS. 


size.  In  the  dog,  from  the  sixth  to  the  ninth  hour  of  digestion,  the 
chief  cells  diminish  in  size  and  contain  fewer  zymogen  granules, 
while  the  parietal  cells  remain  large  and  even  increase  in  size. 
From   the  fifteenth  hour   on,    the   process  becomes   reversed;  the 


Fig.  213. — Section  through  fundus  of  human  stomach  in  a  condition  of  hunger ;   X  S^O' 


Chief  cell. 


Fig.  214. — Section  through  fundus  of  human  stomach  during  digestion  ;   X  5°°- 


chief  cells  enlarge  and  the  parietal  cells  diminish  in  size.  In  a  con- 
dition of  hunger  the  cells  of  the  pylorus  are  clear,  of  medium  size, 
and  do  not  begin  to  enlarge  until  six  hours  after  feeding.  From 
the  fifteenth  hour  on,  the  cells  become  smaller  and  more  turbid, 


THE    STOMACH    AND    INTESTINE. 


273 


Fie  2l5.-Illustrations  of  models,  made  after  Born's  wax-plate  reconstmctio n 
method  of  glandular  structures  and  duodenal  villi  of  the  human  intestine  ;  X  100  .,, 
Fundus  glafd;  i>,  three  pyloric  glands;  the  one  at  the  left  is  a  simple  tubular  gland, 
the  middle  one  a  branched  tubulo-alveolar  gland  ;  the  one  at  the  right  a  typical  pyloric 
gland  of  the  branched  tubular  variety  ;  .,  leaf-shaped  villi  and  crypts  of  Lieberkuhn  of 
the  duodenum;  d,  crypts  of  Lieberkühn  of  the  large  intestine. 
18 


2/4  THE    DIGESTIVE    ORGANS. 

while  the  nuclei  return  to  the  center  of  the  cells.  Since  chemic 
examination  has  shown  that  the  amount  of  pepsin  found  in  the  gas- 
tric mucous  membrane  increases  with  the  enlargement  of  the  chief 
cells  of  the  body  of  the  fundus  glands,  and  decreases  with  their 
diminution  in  size,  there  can  be  hardly  any  doubt  that  this  ferment 
is  elaborated  by  these  cells.  It  is  assumed  that  the  parietal  cells 
secrete  the  acid  of  the  gastric  juice,  although,  in  spite  of  all  efforts, 
it  has  not  yet  been  definitely  proved  that  these  cells  possess  an  acid 
reaction. 

The  vascular  and  lymph-vessels  of  the  stomach,  and  also  its 
nerve  supply,  will  be  considered  in  a  general  discussion  of  these 
structures  pertaining  to  the  entire  intestinal  canal. 

3.  THE  SMALL  INTESTINE. 

The  mucous  membrane  of  the  small  intestine  is  characterized 
by  the  presence  of  villi.  The  villi  vary  in  size  and  shape  in  the 
different  mammals.  In  man,  in  the  upper  portion  of  the  small  in- 
testine, they  are  distinctly  leaf-shaped,  being  three  to  four  times  as 
broad  in  one  direction  as  they  are  in  the  other,  often  showing  a 
narrowing  at  their  bases.  This  has  been  shown  by  reconstruction 
of  the  mucosa  and  a  number  of  villi  from  the  duodenal  region  of 
a  well-preserved  human  intestine.  The  villi  are  of  columnar  shape 
in  the  jejunum,  and  club-shaped  in  the  ileum.  The  mucous  mem- 
brane also  forms  permanent  folds  in  both  the  duodenum  and  the 
remainder  of  the  small  intestine,  the  valvulae  conniventes  (Kerk- 
ring).  Upon  these  the  villi  rest,  and,  indeed,  it  is  probable  that  the 
very  existence  of  the  plicae  is  due  to  the  blending  of  the  basilar 
ends  of  the  villi. 

The  epithelium  of  the  intestinal  mucous  membrane  covers  the 
villi  in  a  continuous  layer,  and  penetrates  into  the  mucosa  to  form 
the  glands.  Its  structure  is  essentially  the  same  in  all  regions  of 
the  small  intestine,  the  cells  being  of  the  high  columnar  variety  with 
free  surfaces  covered  by  wide,  striated  cuticular  borders.  The 
basilar  portions  of  these  cuticular  borders  are  nearly  always  homo- 
geneous, and  upon  vertical  section  give  the  appearance  of  a  fine  line. 
The  cuticular  borders  of  adjacent  cells  blend  with  each  other,  form- 
ing a  continuous  membrane,  large  areas  of  which  may  be  detached 
from  the  villi  (cuticula).  The  body  of  the  cell  consists  of  a  fine 
fibrillar  structure  (spongioplasm)  with  the  main  threads  parallel  to 
long  axis  of  the  cell.  This  is  more  distinct  in  the  free  portions  of 
the  cell.  In  the  interfibrillar  substance  are  found  fine  granules. 
The  nuclei  lie  usually  in  the  basilar  third  of  the  cells,  and  only 
where  they  show  mitoses,  as,  for  instance,  in  the  tubular  intestinal 
glands,  do  they  pass  to  the  free  ends  of  the  cells.  The  basal  ends 
of  the  epithelial  cells  in  the  small  intestine  are  also  seen  to  be 
pointed,  and  the  probability  is  that  they  rest  upon  the  basement 
membrane.      The  question  has,  however,  not  been  fully  settled. 


THE    STOMACH    AND    INTESTINE. 


275 


The  epithelial  cells  undergo  a  special  metamorphosis,  after 
which,  by  an  increased  production  of  mucus,  they  change  into  gob- 
let cells.  From  recent  investigations  it  would  seem  that  any 
epithelial  cell,  whether  it  be  situated  upon  the  upper  surface  of  a 
villus  or  deep  down  in  one  of  the  tubules  of  the  intestinal  glands,  is 
capable  of  transformation  into  a  goblet  cell.  The  number  of  goblet 
cells  is  subject  to  great  variation  ;  they  are  found  singly  in  small 
numbers,  or  are  very  numerous,  according  to  the  stage  of  digestion 
and  quantity  of  food  in  the  intestine.  The  manner  in  which  an 
ordinary  epithelial  cell  changes  into  a  goblet  cell  is  very  easily 
explained  if  the  mechanical  action  on  the  cell  caused  by  an  accumu- 
lation of  secretion  be  taken  into  consideration.  As  the  secretion 
increases  in  quantity  the  upper  portion  of  the  cell  becomes  distended, 
and  the  remains  of  the 
protoplasm,  together 
with  the  nucleus,  are 
pushed  toward  the  nar- 
row base  of  the  cell  ; 
the  cuticular  zone  is 
stretched,  bulges  into 
the  lumen  of  the  intes- 
tine, and  is  finally  perfor- 
ated, and  perhaps  even 
thrown  off.  In  this  way 
the  cell  loses  its  mucous 
secretion,  collapses,  and 
then  appears  as  a  thin, 
almost  rod  -  like  struc- 
ture, with  a  long  nu- 
cleus. It  is  the  gener- 
ally accepted  theory  that 
such  an  empty  goblet 
cell  may  again  assume 
the  shape  of  an  ordinary 
epithelial  cell  and  repeat 
the  process  just  de- 
scribed. 

Leucocytes  are  some- 
times found  within  the 
epithelial  cells,  but  more 
usually  between  them, 
and  according  to  Stöhr 
(84,  89,  94),  when  seen 
in  these  positions,  are 
in  the  act  of  migrating 
into  the  lumen  of  the  intestine.  That  some  of  these  cells  actually 
pass  into  the  lumen  is  probably  true  ;  but  as  yet  no  leucocytes  have 
ever  been  observed  in  the  cuticula  itself,  and  neither  is  the  number 


Mucosa. 


Muscularis 
mucosa;. 


Fig.  216. — Section  through  mucous  membrane 
of  human  small  intestine ;  X  ^^-  At  (7  is  a  col- 
lapsed chyle-vessel  in  the  axis  of  the  villus. 


i^e 


THE    DIGESTIVE    ORGANS. 


fundus  of  the  glands. 


of  cells  found  in  the  lumen  of  the  intestine  proportionate  to  the  leuco- 
cytes  present  in  the  epithelium.  Since  many  are  seen  in  the  epithe- 
lium undergoing  kaiyokinetic  division,  it  is  more  probable  that  a 
part  of  them  actually  wander  into  the  epithelium  for  the  purpose  of 
division  (Chemotaxis  ?),  only  to  return  to  the  mucosa  after  the  com- 
pletion of  the  process  (compare  p.  6i). 

Into  the  spaces  between  the  villi  open  numerous  tubular  glands. 
These  are  seldom  branched,  and  are  known  as  Lieb  er  kühn'  s  glands, 
or  crypts.  Their  length  varies  from  320  ^i  to  450  ^.  They  are 
regularly  arranged  in  a  continuous  row,  and  often  have  an  ampulla- 
like widening  of  their  lumina  extending  almost  to  the  muscularis 
mucosae,  but  never  quite  reaching  it.  They  are  uniformly  distrib- 
uted not  only  throughout  the  small  intestine,  but  also  throughout 
the  large  intestine  and  rectum.      The  cells  lining  the  crypts  of  the 

small  intestine  are  about 
one-half  as  long  as  those 
covering  the  villi ;  a  cuticu- 
lar  border  is  seen  on  the 
cells  lining  the  upper  part 
of  the  glands,  but  is  ab- 
sent in  the  cells  lining  the 


The 
cells  are  conical  in  shape, — 
a  condition  probably  due 
to  the  curvature  of  the 
glandular  wall, — the  base 
of  each  cone  lying  toward 
the  basement  membrane, 
the  apex  toward  the  lumen 
of  the  gland — a  condition 
opposite  to  that  found  in 
the  villi.  Numerous  goblet 
cells  are  also  present.  They 
vary  only  slightly  in  shape 
during  mucous  secretion, 
and  do  not,  as  in  the  villi, 
assume  the  form  of  goblets 
with  distinct  pedicles.  Mito- 
ses are  always  seen  in  the 
intestinal  glands,  especially 
in  cells  which  do  not  con- 
tain mucin.  They  are 
readily  distinguished,  since 
the  nuclei  in  process  of  division,  as  we  have  seen,  lie  outside  of  the 
row  formed  by  the  remaining  nuclei.  The  plane  of  division  in 
these  cells  lies  horizontal  to  the  long  axis  of  the  gland,  so  that  an 
increase  in  the  number  of  cells  results  in  an  increase  in  the  area  of 
the  glandular  walls.      Mitoses  are  very  rarely  observed  in  the  epi- 


Fig.  217. — Longitudinal  section  through  sum- 
mit of  villus  from  human  small  intestine  ;  X  9°° 
(Flemming's  solution)  :  At  0'  is  the  tissue  of  the 
villus  axis  ;  b^  epithelial  cells  ;  c,  goblet  cell ;  d, 
cuticular  zone. 


THE    STOMACH    AND    INTESTINE 


2/7 


thelium  covering  the  villi.      If,  therefore,  an\'  cells  be  destroyed  on 
the  surface  of  the  villi,  it  must  be  assumed  that  the  loss  is  replaced 
by  new  elements  pushed  up  from  the  glands  below  (Bizzozero    89 
92,  I). 

In  the  fundus  of  the  crypts  of  Lieberkühn  of  the  small  intes- 
tine are  also  found  a  variety  of  cells  first  described  by  Paneth,  and 
known  as  the  cells  of  Paneth.  These  cells  contain  granules  which 
stain  readily  in  eosin  and  in  iron-lac-hematoxylin,  and  are  no 
doubt  cells  which  contain  zymogen  granules,  cells  which  elaborate 
an  enzyme.  In  the  opossum  the  cells  of.  Paneth  are  found  not 
only  in  the  crypts  but  also  in  epithelium  of  the  villi  intermixed 
with  the  columnar  cells  and  goblet  cells  (Sidney  Klein). 

The  entire  duodenum,  as  well  as  that  part  of  the  pylorus  in  the 
immediate  vicinity  of  the  pyloric  valve,  is  characterized  by  the 
presence  of  glands  of  a  second  type.  In  the  duodenum  these  are 
seen  intermingled  with  the  glands  of  Lieberkühn,  and  in  the  pylorus 
with  the  pyloric  glands.  These  glands,  Brumier's  glands,  have  a 
diameter  of  from  0.5  to  i  mm.,  and  are  branched  tubulo-alveolar 
glands,  with  tubules  provided  with  alveoli,  especially  along  their 
lower  portions.  The  bodies  of  the  glands  are  situated  principally 
in  the  submucosa,  although  a  part  may  be  in  the  mucosa.  In  the 
stomach  they  open  into  the  gastric  crypts,  in  the  intestine  either  in- 
dependently between  the  villi,  or  into  the  glands  of  Lieberkühn. 
Here  the  glandular  cells  are  in  general  similar  to  those  of  the 
pyloric  glands,  although,  as  a  rule,  somewhat  smaller  than  the 
latter.  The  secretion  of  these  glands  is  mucus  (Bensley).  Just 
as  the  duodenal  glands  extend  into  the  stomach,  so  also  the  pyloric 
glands  of  the  latter  are  found  in  the  upper  portion  of  the  duodenum. 
Besides  short  villi,  there  are  also  present  in  the  duodenum  depres- 
sions of  the  mucous  membrane  analogous  to  the  gastric  crypts.  The 
glands  of  Lieberkühn  begin  at  a  certain  distance  from  the  pylorus  ; 
at  first  they  are  short,  and  do  not  attain  their  customary  length  until 
a  point  is  reached  at  which  the  pyloric  glands  extending  into  the 
duodenum  finally  disappear  (znd.  Fig.  218).  It  is  therefore  obvious 
that  a  transition  zone  exists  between  pylorus  and  duodenum,  and 
that  a  distinct  boundary  line  can  not  be  drawn  between  the  two,  at 
least  so  far  as  the  mucous  membrane  is  concerned.  The  duodenal 
glands,  as  their  name  would  indicate,. are  present  only  in  the  duod- 
enum. Between  the  jejunum  and  ileum  there  is  no  distinct  boundary, 
not  even  when  microscopically  examined.  The  differences  are  mostly 
of  a  quantitative  nature  ;  in  the  jejunum  the  valvulae  conniventes  are 
more  numerous  than  in  the  ileum,  and  the  villi  more  slender  and 
closer  together.  The  glands  of  Lieberkühn  also  appear  to  be  more 
numerous  in  the  jejunum. 

The  mucosa  of  the  small  intestine  consists  of  reticular  adenoid 
tissue  containing  mononuclear  lymphocytes,  polymorphonuclear 
leucocytes,  and  leucocytes  with  granular  protoplasm.  It  sup- 
ports   the    glands    and    extends    into    the    villi     whose    axes    it 


2/8 


THE    DIGESTIVE    ORGANS. 


forms.  The  mucosa  is  separated  from  the  glands,  from  the 
epithelium  of  the  villi,  as  well  as  from  that  of  the  remain- 
ing   surface    of  the   intestine    by   a  peculiar    basement   membrane. 


Longitudinal 
muscular 
layer. 


Sphincter 
pylori. 


Submucosa. 


■  Brunner's 
glands. 


Lymph- 
nodule. 


Villus. 


Circular  mus-'^V;;;-.^ 
cular  layer. ' 


•ÄQ%i--  a 
'    S^^^ —  Muscularis  mucosae. 


~^^^^  ""  Submucosa. 


Villus. 


Brunner's  glands. 


■•glands  of  Lieberkühn. 


Fig.  2l8. — Section  through  the  junction  of  the  human  pylorus  and  duodenum  ;  X  about 
15  :  At  a  the  pyloric  glands  extend  into  the  duodenum. 

The  latter  somewhat  complicates  a  proper  histologic  analysis,  and 
as  a  consequence  opinions  regarding  its  structure  and  significance 
vary  considerably.  By  some  it  has  been  described  as  a  homo- 
geneous, hyaline,  and  exceedingly  fine  membrane  containing  nuclei, 
by  others  as  a  lamella  consisting  entirely  of  endothelial  cells.  At 
all  events,  there  are  certainly  nuclei  in  the  basement  membrane. 
Beneath  the  basement  membrane  is  a  marginal  layer  of  a  more 
fibrillar  character.     This  is  closely  associated  with  the  mucosa,  and 


THE    STOMACH    AND    INTESTINE. 


279 


may  be  regarded  as  a  differentiation  of  the  latter.  Toward  the 
muscularis  mucosae  the  mucosa  is  terminated  by  a  reticulated  elastic 
membrane  (F.  P.  Mall,  in  the  dog),  containing  openings  for  the 
entrance  of  vessels,  nerves,  and  muscle-fibers. 

The  muscularis  imicoscB  consists  of  two  layers  of  unstriped 
muscular  fibers  arranged  in  a  manner  similar  to  that  in  the  external 
muscular  tunic — /.  e.,  having  an  inner  circular  and  an  outer  longi- 
tudinal layer.  The  fibers  are  frequently  gathered  into  bundles, 
which  appear  to  be  separated  from  each  other  by  connective  tissue. 
From  both  layers,  but  more  especially  from  the  inner,  muscle-fibers 
are  given  off  at  right  angles,  which  enter  the  tunica  propria  and 
pass  between  the  glands  of  Lieberkühn,  and  even  into  the  villi. 
In  the  latter  these  muscle-fibers  are  arranged  in  bundles,  and  lie 


Epithelium.   -- 


Submucosa.  - 


S~^::ä~;s    ^~=S^i^' 


Fig.   219. — Section  of  soli 


;ction  of  solitary  lymph-nodule  from  vermiform  appendix  of  guinea- 
pig,  showing  crypt ;  X  about  400  (Flemming's  fluid). 


near  their  axes  around  the  lacteal  vessels.     The  contraction  of  these 
fibers  causes  a  contraction  of  the  entire  villus. 

Lymph-nodules  are  distributed  throughout  the  mucosa  of  the 
small  intestine,  occurring  either  singly,  as  solitary  follicles,  or 
aggregated,  as  Peyer's  patches.  At  the  points  where  they  occur, 
the  villi  are  absent  and  a  lateral  displacement  of  the  glands  of 
Lieberkühn  is  observed.  The  lymph-nodule  is  usually  pyriform  in 
shape.  The  thinner  portion  protrudes  somewhat  in  the  direction 
of  the  lumen  of  the  intestine,  while  the  thicker  portion  extends 
outward  to  the  muscularis  mucosae,  the  latter  being  frequently  in- 
dented or  even  perforated  if  the  lymph-nodules  be  markedly  devel- 
oped. Their  structure  is  similar  to  that  of  the  lymph-follicles  (see 
under  these),  and  consists  of  reticular  adenoid  tissue,  supporting 


28o 


THE    DIGESTIVE    ORGANS. 


lymph-cells.  It  should  be  remembered  that  every  nodule  may 
possess  a  germ  center.  Peyer's  patches  are  collections  of  these 
lymph-follicles.  The  surface  of  the  nodule  presenting  toward 
the  lumen  of  the  intestine  is  covered  with  a  continuous  layer  of 
intestinal  epithelium.      In  man  the  summit  of  that  portion  of  the 


Intestinal  epithelium. 


—  Lumen  of  gland. 


-  Goblet  cell. 


Mucosa. 


-     Mucosa. 


—     Muscularis  mucosae. 


Fig.  220. — From  colon  of  man,  showing  glands  of  Lieberkühn  ;  X  200. 

nodule  projecting  into  the  lumen  of  the  intestine  presents  but  a 
slight  depression  of  the  intestinal  epithelium,  while  in  some  animals 
(guinea  -  pigs),  and  especially  in  the  nodules  composing  Peyer's 
patches,  there  is  a  deeper  depression,  even  leading  to  the  formation 
of  a  so-called  "crypt"  or  "lacuna"  {vid.  Fig.  219).  At  the 
summit,  the  intestinal  epithelium  where  it  comes  in  contact  with 
the  lymph-nodule,  is  peculiarly  altered.  In  most  cases  there  is 
an  absence  of  a  basement  membrane,  the  epithelium  resting 
directly  upon  the  lymphoid  tissue.  No  clearly  defined  boundary 
between  the  two  is  distinguishable  (intermediate  zone  of  v.  David- 
ofif )  ;  they  are  therefore  in  the  closest  relationship  to  each  other. 
The  basal  surfaces  of  the  epithelial  cells  are  fibrillar,  the  fibrils 
seeming  to  penetrate  into  the  adenoid  reticulum  of  the  follicles. 


THE    STOMACH    AND    INTESTINE. 


281 


4.  THE  LARGE  INTESTINE,  RECTUM,  AND  ANUS. 

The  small  intestine  ends  at  the  ileocecal  valve.  At  some  dis- 
tance from  the  margin  of  the  valve  the  villi  of  the  ileum  become 
broad  and  low.  In  the  immediate  vicinity  of  the  valve  their  basilar 
portions  become  confluent,  forming'a  honeycomb  structure  which 
supports  a  few  villi.  At  the  base  of  the  honeycomb  open  the  glands 
of  Lieberkühn.  On  the  cecal  side  of  the  valve  the  villi  become 
fewer  in  number  and  finally  disappear,  while  the  folds  which  give 
the  honeycomb  appearance  persist  for  a  considerable  distance.      In 


Fig.    221. — Transverse   section  of   human   vermiform   appendix;    X  20.      Observe   the 
numerous  lymph  nodules.      The  clear  spaces  in  the  submucosa  are  adipose  tissue. 


the  adult  cecum  the  villi  are  absent.  The  mucosa  and  glands  pre- 
sent a  structure  similar  to  that  of  the  remainder  of  the  large  intes- 
tine. In  the  mucosa  of  the  vermiform  appendix  is  found  a  relati\"el}' 
large  number  of  solitary  lymph-follicles,  occasionally  forming  a 
continuous  layer.  The  marked  development  of  the  lymph-follicles 
encroaches  upon  the  glands  of  Lieberkühn,  so  that  many  are 
obliterated  ;  they  are  penetrated  by  the  adenoid  tissue,  the  epithe- 
lial cells  of  the  glands  mingling  with  the  lymph-cells.  What  finally 
becomes  of  the  secretory  cells  has  not  been  definitely  ascertained 
(Rüdinger,  91). 


282 


THE    DIGESTIVE    ORGANS. 


In  the  colon  the  villi  are  wanting,  while  the  glands  of  the 
mucosa  are  densely  placed  and  distributed  with  regularity. 

The  glands  of  Lieberkühn  in  the  colon  are  somewhat  longer, 
and  as  a  rule  contain  many  more  goblet  cells  than  those  in  the  small 
intestine.  Only  the  neck  and  fundus  of  the  glands  show  cells  de- 
void of  mucus.  Transitional  stages  between  the  latter  and  the 
goblet  cells  have  been  observed  in  man  (Schaffer,  91).  Solitary 
lymph-follicles  are  found  throughout  the  colon.  They  are  situated 
in  the  mucosa,  only  the  larger  ones  extending  into  the  submucosa. 
The  glands  of  Lieberkühn  are  displaced  in  the  regions  of  the  lymph- 
follicles. 


Submu- 
cosa. 


Fig.  222.^ — A  solitary  lymph-follicle  from  the  human  colon  :  At  a  is  seen  a  pronounced 
concentric  arrangement  of  the  lymph-cells. 


The  tcenicE  and  plicce  semilunares  cease  at  the  sigmoid  flexure, 
and  are  replaced  in  the  rectum  by  the  plicce  transversales  recti. 
Permanent  longitudinal  folds,  the  so-called  coliimnce  rectales  Mor- 
gagni, are  present  only  in  the  lower  portion  of  the  rectum.  Here  the 
intestinal  glands  are  longest  but  disappear  simultaneously  with 
the  rectal  columns.  At  the  anus  the  mucous  membrane  of  the 
rectum  forms  a  narrow  ring  devoid  of  glands,  covered  by  stratified 
pavement  epithelium,  and  terminating  in  the  skin  in  an  irregular 
line.  The  transition  from  the  mucous  membrane  to  the  skin  is 
gradual,  yet  reminding  one  of  the  appearance  presented  at  the 
junction  of  the  esophagus  with  the  cardiac  end  of  the  stomach. 

External  to  the  anus,  and  at  a  distance  of  about  one  centimeter 
from  it,  are  numerous  highly  developed  sweat-glands,  the  circum- 
anal glands  of  Gay,  which  are  almost  as  large  as  the  axillary 
glands ;  also  sweat-glands  of  a  peculiar  type,  in  that  they  show  a 
branching  of  the  tubules  (see  Sweat-glands,  under  Skin). 


THE    STOMACH    AND    INTESTINE. 


283 


5.  BLOOD,  LYMPH,  AND  NERVE  SUPPLY  OF  THE  INTESTINE. 

In  general,  the  following  holds  true  with  regard  to  the  blood- 
vessels of  the  intestinal  tract  (further  details  will  be  discussed  in 
dealing  with  the  vessels  of  the  various  regions  of  the  intestine) : 
The  arteries  enter  along  the  line  of  the  mesenteric  attachment  and 
penetrate  the  longitudinal  muscular  layer.  Between  the  two  mus- 
cular layers  branches  are  given  off  which  form  an  intermuscular 
plexus,  from  which,  in  turn,  smaller  branches  pass  out  to  supply 
the  muscles  themselves.  The  arterial  trunks  penetrate  the  circu- 
lar muscular  layer  and  form  an  extensive  network  of  larger 
vessels  in  the  deeper  layer  of  the  submucosa.  This  is  known 
as  Heller's  plexus  (F.  P.  Mall).     From  this,  radiating  branches  are 


— -  Epithelium  of 
stomach. 


Region  of  the 
bodies  of  the 
gastric  glands. 


Muscularis  mucosae. 


Fig.  223. — Section  through  fundus  of  cat's  stomach.     The  blood-vessels  are 
injected ;  X  ^o- 


given  off  which  supply  the  muscularis  mucosae,  forming  under 
the  latter  a  close  network  of  finer  vessels.  This  plexus,  together 
with  that  of  Heller,  gives  rise  to  vessels  which  penetrate  the  mus- 
cularis mucosae  and  break  up  into  capillaries  in  the  mucous  mem- 
brane. The  veins  of  the  mucous  membrane  form  beneath  the 
muscularis  mucosae  a  plexus  with  small  meshes,  giving  off  many 
radiating  branches  ;  these  in  turn  unite  to  form  an  extensive  net- 
work of  coarser  vessels.  Veins  extend  from  the  latter  and  unite 
to  form  larger  trunks,  which  then  lie  side  by  side  with  the  arteries. 
According  to  F.  P.  Mall,  delicate  retia  mirabilia  occur  here  and 
there  in  the  venous  network  in  the  submucosa  of  the  intestine  of 
the  dog. 

In  the  esophagus  the  arteries  end  in  a  capillary  network  situated 


284  THE    DIGESTIVE    ORGANS. 

in  the  mucosa  and  extending  into  the  connective -tissue  papillae  of 
the  mucosa. 

The  vessels  of  the  stomach  are  arranged  in  plexuses  in  the 
muscular  coat,  submucosa,  and  beneath  the  muscularis  mucosae,  as 
previously  described.  From  the  plexus  beneath  the  muscularis  mu- 
cosae, small  branches  are  given  off  which  pass  through  this  layer  and 
in  the  mucosa  form  a  capillary  network,  consisting  of  relatively  small 
capillaries,  which  surround  the  gastric  glands,  this  plexus  being  par- 
ticularly well  developed  in  the  region  around  the  body  and  neck  of 
the  glands,  where  the  parietal  cells  are  most  numerous.  The  capil- 
laries of  this  network  are  continuous  with  capillaries  of  a  much  larger 
size,  forming  a  network  surrounding  the  gastric  crypts  and  situated 
immediately  under  the  epithelium  lining  the  mucosa  of  the  stomach. 
The  blood  is  collected  from  this  capillary  plexus  by  small  veins 
which  pass  nearly  perpendicularly  through  the  mucosa,  forming  a 
plexus  above  the  muscularis  mucosae,  from  which  small  veins  pass 
through  the  muscularis  mucosae  to  the  venous  plexus  in  the  sub- 
mucosa. 

The  blood-vessels  of  the  mucosa  of  the  small  intestine  may  be 
divided  into  (i)  the  arteries  of  the  villi  and  (2)  the  arteries  of  the 
intestinal  glands.  The  former  arise  principally  from  the  deep  arterial 
network  in  the  submucosa,  then  penetrate  the  muscularis  mucosae 
and  give  off  branches  at  acute  angles  which  continue  without 
further  branching  into  the  summits  of  the  villi.  Within  the  villi 
themselves  the  arteries  lie  in  the  axes.  The  broader  villi  may 
contain  two  arteries.  The  circular  muscle-fibers  of  the  arteries 
gradually  disappear  inside  of  the  villi  (dog),  and  at  the  summit  of 
the  latter  the  vessels  break  up  into  a  large  number  of  capillaries. 
These  form  a  dense  network  extending  beneath  the  basement  mem- 
brane and  into  its  marginal  layer.  These  networks  give  rise  to 
venous  capillaries  which  unite  to  form  small  vessels  and  finally  end 
in  two  or  more  larger  veins  inside  of  the  villi.  These  latter  are  con- 
nected with  the  venous  network  in  the  mucosa. 

The  glandular  arteries,  derived  principally  from  the  superficial 
network  of  the  submucosa,  also  pass  through  the  muscularis 
mucosae  and  break  up  internally  into  capillary  nets  which  encircle 
the  intestinal  glands  ;  these  give  rise  to  small  veins  which  empty 
into  the  venous  plexus  of  the  mucosa.  The  veins  of  the  plexus  in 
the  mucosa  unite  to  form  larger  branches,  which  connect  with  the 
plexus  in  the  submucosa  (compare  Fig.  224).  In  the  dog  these 
trunks  inside  of  the  muscularis  mucosae  are  encircled  by  bundles  of 
muscle-fibers  (sphincters,  F.  P.  Mall).  The  capillaries  of  the  solitary 
lymph-nodules  do  not  always  penetrate  into  the  centers  of  the  latter, 
but  often  leave  a  central  nonvascular  area. 

The  blood-vessels  of  the  mucosa  of  the  large  intestine  are,  in 
their  distribution,  similar  to  the  glandular  vessels  of  the  small  intes- 
tine and  stomach. 

The  lymph-vessels  begin  in  the  mucosa  near  the  epithelium,  pass 


THE    STOMACH    AND    INTESTINE. 


285 


down  between  the  glands,  and  are  arranged  in  the  form  of  a  net- 
work just  above  the  muscularis  mucosas,  but  with  coarser  meshes 
than  that  formed  by  the  blood-vessels.  Here  the  valves  begin  to 
make  their  appearance.  The  lymph-vessels  pass  through  the  mus- 
cularis mucosae  and  in  the  outer  portion  of  the  submucosa  form  a 
plexus  with  open  meshes,  from  which  are  derived  the  efferent  ves- 
sels which  penetrate  the  muscular  coat  and  thus  gain  access  to  the 
mesentery.  In  their  course  through  the  muscular  coat  they  com- 
municate with  the  branches  of  a  plexus  of  lymph-vessels  situated 
between  the  two  muscular  layers,  and  also  with  lymph-vessels  found 
in  the  serous  coat. 


Central  chyle- 
vessel  of  vil- 
lus. 


Artery. 


--fi-    Chyle-vessel. 


Mucosa. 

Muscularis 

mucosas. 

Submucosa. 

Plexus  of 
lymph  -ves- 
sels. 

Circular  mus- 
cular layer. 

Ple.vus  of 
lymph-ves- 
sels. 

Long.  muse. 

layerwiththe 

serous  coat. 


Fig.  224. — Schematic  transverse  section  of  the  human  small  intestine  (after  F.  P.  Mall). 


The  lymphatics  of  the  small  intestine  begin  in  the  axes  of  the 
villi.  When  filled,  these  lymph-vessels  are  conspicuous,  irregularly 
cylindric  capillary  tubules,  lined  by  endothelial  cells,  and  known  as 
the  axial  canals,  the  chyle-vessels,  or  the  lacteals  of  the  villi.  They 
are  hardly  discernible  when  collapsed.  If  the  villus  be  broad,  it 
may  contain  two  chyle-vessels,  which  then  join  at  the  apex  of  the 
villus,  and  may  also  be  connected  with  each  other  b}'  a  few  anasto- 
moses. At  the  base  of  the  villus  the  chyle-vessel  enters  a  h-mphatic 
capillary  network,  the  structure  of  which  is   due  to  the  confluence 


286  THE    DIGESTIVE    ORGANS. 

of  similar  canals.  Numerous  lymph-vessels  from  this  network 
penetrate  the  mucous  membrane  in  a  vertical  direction,  uniting  at 
the  bases  of  the  intestinal  glands  to  form  a  second  plexus — sub- 
glandular  plexus  of  the  mucosa.  A  few  of  the  lymph-vessels  pene- 
trating the  mucous  membrane  directly  perforate  the  muscularis 
mucosae  to  join  the  lymphatic  network  of  the  submucosa.  The 
subglandular  plexus  also  communicates  with  the  submucous 
lymphatic  plexus  by  means  of  small  radiating  branches  {vid.  Fig. 
224).  The  solitary  lymph-nodules  themselves  contain  no  lymphatic 
vessels,  but  are  encircled  at  their  periphery  by  a  network  of  lymph 
capillaries.  The  same  is  true  of  the  nodules  in  Peyer's  patches. 
It  is  an  interesting  fact  that  in  the  rabbit  lymph-sinuses  exist 
around  Peyer's  patches,  giving  to  the  latter  a  still  greater  similarity 
to  the  nodules  of  lymph-glands.     The  solitary  nodules  of  the  same 


Fig.  225. — A  portion  of  the  plexus  of  Auerbach  from  stomach  of  cat,  stained  with 
methylene-blue  (intra  vitat?i),  as  seen  under  low  magnification. 

animal  are   not  surrounded  by  the  sinuses  just  mentioned  (Stöhr, 

94)- 

The  structures  of  the  alimentary  canal  receive  their  innervation 
mainly  from  sympathetic  neurones,  the  cell-bodies  of  which  are 
grouped  to  form  small  ganglia,  located  at  the  nodal  points  of  two 
plexuses,  one  of  which  is  situated  between  the  two  layers  of  the 
muscular  coat,  the  other  in  the  submucosa.  These  two  plexuses 
are  found  in  the  entire  digestive  tract,  although  not  equally  well 
developed  in  its  different  regions.  The  outer  plexus,  the  more 
prominent  of  the  two,  situated  between  the  two  layers  of  the  muscu- 
lar coat,  is  known  as  the  plexus  myentericus,  or  the  plexus  of  Auer- 
bach. It  consists  of  innumerable  small  sympathetic  ganglia,  united 
by  small  bundles  of  nonmedullated  fibers,  containing  here  and  there 
a  much  smaller  number  of  medullated  nerve-fibers.  The  cell-bodies 
of  the  sympathetic  neurones  of  this  plexus  are  grouped  to  form  the 


THE    STOMACH    AND    INTESTINE. 


'.87 


sympathetic  ganglia.  The  dendrites,  the  number  of  which  varies 
for  the  different  cells,  divide  and  redivide  in  the  ganglia,  some  ex- 
tending into  the  nerve  bundles  uniting  the  ganglia.  The  neuraxes 
of  the  sympathetic  neurones  of  the  ganglia  form  nonmedullated 
nerve-fibers,  which  leave  the  ganglia  by  one  of  the  several  roots 
possessed  by  each  ganglion,  and,  after  repeated  division  and  forming 
intricate  plexuses  in  the  circular  and  longitudinal  layers  of  the  mus- 
cular coat,  terminate  on  the  involuntary  muscle-cells  of  these  layers. 

The  plexus  in  the  submucosa,  known  as  the  plexus  of  Meissner, 
is  similarly  constructed,  although  it  contains  fewer  and  much  smaller 
ganglia  and  the  meshes  of  the  plexus  are  much  finer.  It  commu- 
nicates by  numerous  anastomoses  with  the  plexus  of  Auerbach. 
The  neuraxes  of  the  sympathetic  neurones  of  this  plexus  have  not 
been  traced,  with  any  degree  of  certainty,  to  their  terminations. 
Numerous  nonmedullated  nerves  enter  the  muscularis  mucosae  and, 
according  to  Berkley  (93,  I),  form  in  the  dog  terminal  bulbs  and 
nodules  which  perhaps  rep- 
resent the  endings  of  motor 
(sympathetic)  nerves  in  this 
layer.  Nerve-fibers  have  also 
been  traced  into  the  mucosa, 
and  in  the  vicinity  of  the 
glands  and  in  the  villi  are 
found  numerous  exceedingly 
fine  nerve-fibers  which  inter- 
lace, but  in  the  greater  por- 
tion of  the  intestinal  tract  the 
endings  of  these  fibers  have 
not  been  fully  worked  out. 
That  they  end  on  the  gland- 
cells  seems  very  probable 
from  observations  made  by 
Kytmanow   (96),    who    was 

able,  by  means  of  the  methylene-blue  method,  to  stain  plexuses 
of  fine  nerve-fibrils  surrounding  the  gastric  glands  of  the  cat,  some 
of  these  fibrils  being  traced  through  the  basement  membrane  of 
the  glands  and  to  and  between  the  gland-cells,  where  they  ter- 
minated in  clusters  of  small  nodules  on  both  the  chief  and  parietal 
cells.  The  plexus  of  Meissner  is  not  so  well  developed  in  the 
esophagus  as  in  the  remaining  portions  of  the  digestive  tract. 

That  the  cell-bodies  of  many  of  the  sympathetic  neurones  of 
Auerbach's  and  Meissner's  plexuses  are  capable  of  being  stimulated 
by  cerebrospinal  nerves  seems  certain  from  obser\^ations  made  by 
Dogiel  (95),  who  has  shown  that  many  small  medullated  nerv^e- 
fibers  which  enter  the  digestive  tract  through  the  mesentery  (small 
and  large  intestines)  terminate  after  repeated  division  in  terminal 
end-baskets  which  surround  the  cell-bodies  of  many  of  the  sympa- 
thetic neurones  of  these  plexuses.     Similar   nerve-fibers  ending  in 


Fig.  226. — From  thin  section  of  esophagus 
of  cat,  showing  the  epithelium  and  a  portion 
of  the  mucosa  and  the  terminal  nerve-fibrils  in 
the  epithelium  (from  preparation  of  Dr.  DeWitt). 


288  THE    DIGESTIVE    ORGANS. 

baskets  have  also  been  observed  in  the  gangha  of  the  plexuses  of 
the  stomach  and  esophagus.  Large  medullated  nerve-fibers,  the 
dendrites  of  sensory  neurones,  have  also  been  traced  to  the  alimen- 
tary canal.  In  the  esophagus  these  pass  to  the  mucosa,  where, 
after  repeated  division,  they  lose  their  medullary  sheaths,  the  non- 
meduUated  terminal  branches  forming  a  subepithelial  plexus  from 
which  terminal,  varicose  branches,  further  dividing,  enter  the  strati- 
fied epithelium  and  may  be  traced  to  near  the  surface  of  the  epithe- 
lium. 

Large  medullated  nerve -fibers  may  be  traced  through  the 
ganglia  of  Auerbach's  and  Meissner's  plexuses  in  the  stomach  and 
intestinal  canal  and  through  the  nerve  bundles  uniting  these  ganglia 
(Dogiel,  99),  but  the  termination  of  these  fibers  has  not  been  deter- 
mined. In  the  large  intestine  of  the  cat  they  have  been  traced  to 
the  epithelium  and  between  the  epithelial  cells  covering  the  mucosa 
(Huber). 

6.  THE  SECRETION  OF  THE  INTESTINE  AND  THE  ABSORPTION 

OF  FAT. 

The  cells  of  Brunner's  glands  are  similar  in  many  respects  to 
those  of  the  pyloric  glands.  They  form,  as  has  been  shown,  a 
mucous  secretion,  and  present  in  their  various  physiological  activi- 
ties, structural  changes  which  are  similar  to  the  structural  changes 
presented  by  the  cells  of  other  mucous  glands  under  similar  condi- 
tions (Bensley).  It  is  well  known  that  the  goblet  cells  of  the  in- 
testinal glands  are  very  numerous  during  starvation,  and  that  they 
nearly  disappear  after  continued  functional  activity  ;  furthermore, 
they  entirely  disappear  in  certain  portions  of  the  rabbit's  intestine 
after  pilocarpin-poisoning.  It  would  therefore  appear  that  the  prin- 
cipal physiologic  function  of  the  glands  of  Lieberkühn  is  to  secrete 
mucus,  although  the  possibility  of  the  production  of  another  secre- 
tion, especially  in  the  small  intestine,  must  not  be  excluded  (compare 
R.  Heidenhain,  83),  especially  since  it  has  been  shown  that  the 
cells  of  Paneth  probably  elaborate  an  enzyme. 

Until  recently  it  was  believed  that  the  fat  contained  in  the  food 
was  emulsified  in  the  intestine,  and  furthermore  that  the  bile  acted 
upon  the  cuticular  margins  of  the  epithelial  cells  in  the  villi  in  such  a 
manner  that  an  assimilation  of  the  emulsified  fat  by  the  cells  of  the 
villi  (not  by  the  goblet  cells)  was  made  possible.  It  has  been  re- 
peatedly observed  that  the  epithelial  cells  contained  fat  granules 
during  absorption.  Hence  a  mechanism  was  sought  for  which 
would  account  for  an  assimilation  of  globules  of  emulsified  fat  on 
the  part  of  the  cells.  It  seemed  most  probable  that  protoplasmic 
threads  (pseudopodia)  were  thrown  out  from  each  cell  through  its 
cuticular  zone,  which,  after  taking  up  the  fat,  withdrew  with  it  again 
into  the  cell.  But  when  it  was  shown  that,  after  feeding  with  fatty 
acids  or  soaps,  globules  of  fat  still  appeared  in  the  epithelial  cells  as 
before,  and  that  the  chyle  also  contained  fat,  the  hypothesis  was 


THE   LIVER. 


289 


suggested  that  the  fat  is  split  up  by  the  pancreatic  juice  into  glycerin 
and  fatty  acids,  and  that  the  fatty  acids  are  then  dissolved  by  the 
bile  and  the  alkalies  of  the  intestinal  juice,  only  again  to  combine 
with  the  glycerin  to  form  fat  within  the  epithelial  cells.  It  remains 
for  the  histologist  to  ascertain  the  exact  mechanism  in  the  cell  which 
changes  the  fatty  acids  into  fat.  Altmann  (94)  claims  that  certain 
granules  of  the  cells  (elementary  organisms)  offer  a  solution  to  this 
problem.  The  manner  in  which  the  fat  globules  gain  access  to  the 
lacteal  vessels  of  the  villi  is  a  question  which  has  not  as  yet  been 
settled  definitely  ;  it  would  appear,  however,  that  the  leucocytes 
play  an  important  part  in  this  transfer,  since  in  preparations  of  the 
intestinal  mucosa,  taken  from  an  animal  fed  on  a  diet  rich  in  fat — 
milk  diet — and  stained  in  osmic  acid,  numerous  leucocytes  contain- 
ino-  black  granules  or  globules  may  be  observed  in  the  lacteal 
vessels  and  in  the  spaces  of  the  adenoid  reticulum  of  the  villi. 

D.  THE  LIVER. 

In  the  adult  the  liver  is  a  lobular,  tubular  gland  with  anastomos- 
ing tubules.  When  viewed  with  the  unaided  eye  or  under  low 
magnification  the  liver  is  seen  to  be  composed  of  a  large  number 


Intralobular 
vein. 

Branch  of 

portal  vein. 
Bile-duct, 

Branch  of 

hepatic 

artery. 
Interlobular 

connective 

tissue. 


Fig.  227. — Section  through  liver  of  pig,  showing  chains  of  Hver-cells  ;   X  7°« 


of  nearly  spheric  divisions  of  equal  size  ;  this  is  particularly  notice- 
able in  some  animals,  especially  in  the  pig.  These  divisions  are  the 
liver  lobules  and  have  a  diameter  of  from  0.7  to  2.2  mm.  They  are 
separated  from  each  other  by  a  varying  amount  of  interlobular  con- 
nective tissue,  which  is  a  continuation  of  the  capsule  of  Glissoii,  a 
fibro-elastic  layer  surrounding  the  entire  liver  and  covered  for  the 
greater  portion  by  a  layer  of  mesothelium.  In  the  interlobular 
septa  are  found  the  larger  blood-vessels,  bile  passages,  nen^es  and 
19 


290 


THE    DIGESTIVE    ORGANS. 


lymph-vessels.  On  examining  a  thick  section  of  the  liver  with  a 
low  power,  a  radiate  structure  of  the  lobule  is  noticeable,  and  an 
open  space  is  seen  in  its  center,  which  according  to  the  direction  of 
the  section,  is  either  completely  surrounded  by  liver  tissue  or  con- 
nected  with  the  periphery  of  the  lobule  by  a  canal.  This  open 
space  represents  the  central  or  intralobular  vein  of  the  lobule  which 
belongs  to  the  system  of  the  inferior  vena  cava.  From  the  center 
of  the  lobule  toward  its  periphery  extend  numerous  radiating 
strands  of  cells,  which  branch  freely  and  anastomose  with  each 
other,  and  are  known  as  the  trabecules,  or  cords  of  hepatic  cells.  Be- 
tween the  latter  are  small,  clear  spaces  occupied  partly  by  blood 
capillaries  and  partly  by  the  intralobular  connective  tissue.  The  above 
description  is  in  some  respects  not  a  true  statement  of  the  appear- 
ance presented  by  the  human  liver,  as  in  the  latter  one  or  more 
lobules  may  blend  with  each  other,  thus  rendering  the  individual 
lobules  less  distinct. 

The  hepatic  cords  consist  of  rows  of  hepatic  cells.     The  cells 


'^-^, 


Fig.  228. — Section  through  injected  Hver  of  rabbit.     The  boundaries  of  the  lobules 
are  indistinct ;   X  about  35. 


are  usually  polyhedral  in  form,  with  surfaces  so  approximated  that 
a  cylindric  capillary  space,  known  as  the  bile  capillary  remains  be- 
tween them.  The  angles  of  the  cells  also  show  grooves  which 
join  those  of  the  neighboring  cells  to  form  canals  in  which  lie  the 
blood  capillaries.  A  closer  examination  of  the  hepatic  cells  reveals 
the  fact  that  they  possess  no  distinct  membrane,  and,  in  a  resting 
state,  usually  contain  a  single  nucleus,  although  some  possess  two. 
It  is   an  interesting  fact  that  nearly  all  the  hepatic  cells  of  some 


THE    LIVER. 


291 


animals — as,  for  instance,  the  rabbit — contain  two  nuclei.  The 
cell-bodies  of  the  hepatic  cells,  which  average  from  18//  to  26//  in 
diameter,  show  a  differentiation  into  protoplasm  and  paraplasm. 
This  is  especially  manifest  in  a  state  of  hunger.  In  this  condition 
it  is  seen  that  the  network  of  protoplasm  around  the  nucleus  is  un- 
usually dense,  and  becomes  looser  in  arrangement  as  it  extends 
toward  the  periphery  of  the  cell-body.  The  paraplasm  is  slightly 
granular,  and  contains  glycogen  and  bile  drops  during  the  func- 
tional activity  of  the  cell  (secretion  vacuoles).  The  vacuoles  in  the 
paraplasm  play  an  important  part  in  the  secretion  of  the  cell,  and  are 


Intralobular 
vein. 


Fig.  229, — Human  bile  capillaries.  The  capillaries  of  one  lobule  are  seen  to  anas- 
tomose with  those  of  the  adjoining  lobule  (below,  in  the  figure) ;  X  ^^o  (chrome-silver 
method). 


Vacuole  of  secretion. 

Tubule  of  same. 
Bile  capillary. 


--Vs  >0 


Fig.  230. — Human  bile  capillaries  as  seen  in  section  ;  X  4^0  (chrome-silver  method). 


due  to  the  confluence  of  minute  drops  of  bile  into  a  large  globule. 
As  soon  as  the  vacuole  has  attained  a  certain  size  it  tends  to  empty 


292 


THE    DIGESTIVE    ORGANS. 


its  contents  into  the  bile  capillary  through  a  small  tubule   connect- 
ing the  vacuole  with  the  bile  capillary  (Kupffer,  73,  89). 

The  bile  capillaries  are,  as  we  have  remarked,  nothing  but  tubu- 
lar, capillary  spaces  between  the  hepatic  cells,  with  no  distinct  indi- 
vidual walls,  although  the  outer  portions  of  the  liver  cells  (exo- 
plasm)  are  somewhat  denser  than  the  remainder  of  the  cells, 
and  serve  to  form  a  wall  for  the  bile -capillaries.  They  may  be 
compared  to  the  lumen  of  a  tubular  gland,  although  in  the 
human  liver  their  walls  consist  of  only  two  rows  of  hepatic 
cells.  In  the  lower  vertebrates  the  walls  of  the  bile  capillaries 
appear  in  transverse  section  to  consist  of  several  cells  (in  the 
frog  generally  three,  in  the  viper  as  many  as  five).  The  bile 
capillaries  naturally  follow  the  course  of  the  hepatic  cords — i.  e., 
in  man  extending  radially.  They  form  networks,  the  meshes  of 
which  correspond  to  the  size  of  the  hepatic  cells.  At  the  periphery 
of  the  lobule  the  hepatic  cells  pass  directly  over  into  the  epithelial 
cells  of  the  smaller  interlobular  bile-ducts.  The  epithelium  of  the 
latter  is  of  the  cubical  variety,  its  cells  being  considerably  smaller  than 
the  hepatic  cells.  At  the  point 
where  the  hepatic  cells  become 
continuous  with  the  walls  of  the 
smaller  passages  we  find  a  few 
cells  of  gradually  decreasing  size 
which  represent  a  transition  stage 
from  the  cells  of  the  bile  capil- 


Bile  capillaries. 


Fig.  231. — Schematic  diagram  of  he- 
patic cord  in  transverse  section.  At  the 
left  the  bile  capillary  is  formed  by  four  cells, 
at  the  right  by  two ;  the  latter  type  occurs 
in  the  human  adult. 


Fig.  232. — From  the  human  liver, 
showing  the  beginning  of  the  bile-ducts ; 
X  90  (chrome-silver). 


laries  (hepatic  cells)  to  those  of  the  interlobular  bile  passages. 

The  vascular  system  of  the  liver  is  peculiar  in  that,  besides 
the  usual  arterial  and  venous  vessels  common  to  all  organs, 
there  is  found  another  large  afferent  vein — the  portal  vein.  It 
arises  from  a  confluence  of  the  superior  and  inferior  mesenteric, 
the  splenic,  coronary  veins  from  the  stomach,  and  cystic  veins. 
It  divides  into  two  branches,  the  right  supplying  the  right  lobe  of 
the  Hver,  the  left  the  remaining  lobes.  These  branches  again  divide 
into  numerous  smaller  branches,  the  smallest  of  which  finally  reach 
the  individual  lobules.      Along  its  whole  course  through  the  inter- 


THE    LIVER. 


293 


lobular  connective  tissue  the  portal  vein  and  its  branches  are  accom- 
panied by  divisions  of  the  hepatic  artery  and  bile  passages.  In  a 
transverse  section  of  the  liver  the  arrangement  of  these  structures 
in  the  interlobular  tissue  is  such  that  the  cross-sections  of  the  vessels 
belonging  to  the  hepatic  vein  are  seen  to  be  at  some  distance  from 
the  closeTy  approximated  branches  of  the  portal  vein  and  bile  pas- 
sages. Branches  of  the  portal  vein  encircle  the  liver  lobules  at 
different  points,  and  while  they  remain  within  the  interlobular  con- 
nective tissue,  are  known  as  interlobular  vcms.  From  these,  small 
offshoots  are  given  off  to  the  lobules  which,  on  entering,  divide  into 
capillaries  and  form  a  closely  reticulated  network  between  the 
hepatic  cords.  The  meshes  of  this  network  are  about  as  large 
as  an  hepatic  cell,  each  cell  coming  in  repeated  contact  with  the 
blood  capillaries.  All  of  these  capillaries  pass  toward  the  central 
or  intralobular  vein  of  the  lobule,  which  during  its  efferent  passage 
through  the  lobule  continues  to  receive  capillaries  from  the  portal 


Blood  capillaries. 


Intralobular  vein. 


.  Cord  of  hepatic 
cells. 


Interlobular  vessel. 


Fig.  233. — Injected  blood-vessels  in  liver  lobule  of  rabbit ;  X  ^o^- 


system.  The  intralobular  veins  unite  to  form  the  sublobular  veins, 
situated  in  the  interlobular  connective  tissue,  and  these  unite  to  form 
the  larger  hepatic  veins  which  empty  into  the  inferior  vena  cava. 
The  hepatic  artery  is  of  much  smaller  size  than  the  portal  vein.  It 
is  distributed  in  the  main  to  the  connective  tissue  of  the  liver  and 
to  the  bile-ducts,  breaking  up  into  branches  which  aie  situated 
in  the  interlobular  connective  tissue.  The  terminal  capillaries 
form    small    venules    which    communicate    with     the    interlobular 


294  THE    DIGESTIVE    ORGANS. 

branches  of  the  portal  system.  Whether  the  capillaries  of  the 
hepatic  artery  pass  as  such  into  the  hepatic  lobules  is  difficult  to 
say,  since  injection  masses  forced  into  the  hepatic  artery  pass  over 
into  the  terminal  branches  of  the  portal  vein  and  vice  versa. 
This  question  needs,  therefore,  further  investigation.  The  smaller 
divisions  of  the  hepatic  artery  constitute,  therefore,  internal  radi- 
cals of  the  portal  vein,  since  they  are  within  the  liver  itself 
The  relations  of  the  various  blood-vessels  within  the  lobule  are  in 
themselves  somewhat  difficult  of  comprehension,  but  the  whole  be- 
comes still  more  complicated  when  the  reciprocal  relations  of  the 
vessels  and  bile  capillaries  are  taken  into  consideration.  In  order 
to  understand  the  structure  of  the  liver  lobule,  with  its  hepatic 
cords,  vessels,  and  bile  capillaries,  the  following  points  should  be 
borne  in  mind  :  The  course  of  the  bile  capillaries  is  along  the  sur- 
faces, and  that  of  the  blood-vessels  along  the  angles  of  the  hepatic 
cells  ;  every  cell  comes  in  contact  with  a  bile  capillary  and  a  blood 


Intralobular 
vein. 


Fig.  235, — Reticulum  (Gitterfasern)  of  dog's  liver;  X  ^20  (gold-chlorid  method). 

capillary.  The  latter,  however,  do  not  come  in  contact  with  the 
former,  but  in  man  are  separated  by  at  least  half  the  breadth  of  a 
hepatic  cell.  In  animals  in  which  the  bile  capillaries  are  bounded 
by  more  than  two  cells,  the  blood-vessels  extend  along  the  outer 
sides  of  the  hepatic  cells  ;  here  the  bile  and  blood  capillaries  are 
separated  from  each  other  by  the  breadth  of  a  whole  cell. 

The  connective  tissue  within  the  hepatic  lobules  presents  points 
of  interest  which,  however,  are  not  demonstrable  in  organs  treated 
by  ordinary  methods.  But  when  the  liver  tissue  is  treated  by  a 
certain  special  method. (see  page  307),  an  astounding  number  of  fibers 
are  seen  extending  in  regular  arrangement  from  the  periphery  toward 
the  central  vein.     These  fibers  are  extremely  delicate,  of  nearly 


THE    LIVER.  295 

equal  size,  and  intermingle  in  such  a  manner  as  to  form  an  envel- 
oping network  about  the  blood  capillaries  (Gitterfasern  ;  Kupffer  ; 
Oppel,  91  ;  vid.  Fig.  235).  A  few  coarser  fibers  (radiate  fibers, 
Kupffer,  73)  seem  to  enter  in  a  less  degree  into  the  formation  of  the 
sheath  around  the  blood  capillaries  ;  they  also  extend  from  the 
periphery  toward  the  center  of  the  lobule  and  form  a  coarse  reticu- 
lum, the  meshes  of  which  are  drawn  out  radially.  The  radiate 
fibers  are  less  prominent  in  man,  but  are  numerous  and  well  devel- 
oped in  animals  (rat,  dog).  With  what  exuberance  the  intralobular 
connective  tissue  may  develop,  is  seen  in  the  accompanying  sketch 
of  a  sturgeon's  liver,  which  is  taken  from  one  of  Kupffer's  prepara- 


Connective-tissue 
fibers. 


Fig.  236. — Connective  tissue  from  liver  of  sturgeon.    At  a  is  an  open  space  from  which 
the  hepatic  cells  were  mechanically  removed  during  treatment. 

tions.  The  Gitterfasern  of  Kupffer  are,  as  has  been  shown  by  F. 
P.  Mall,  reticular  fibrils,  presenting  the  same  characteristics  as  similar 
fibrils  found  in  other  regions. 

Certain  peculiar  cells — the  so-called  stellate  cells  of  Kupffer 
{y6) — occur  in  the  lobule,  and  are  seen  only  after  a  special 
method  of  treatment.  They  are  uniformly  distributed,  of  differ- 
ent shapes,  elongated,  and  end  in  two  or  three  pointed  projec- 
tions. They  are  smaller  than  the  hepatic  cells,  and  contain  one  or 
two  nuclei. 

In  a  recent  communication  Kupffer  (99)  states  that  the  stellate 
cells  belong  to  the  endothelium  of  the  intralobular  capillaries  of  the 
portal  vein.  These  capillaries,  which  are,  according  to  their  devel- 
opment, sinusoids  (Minot),  form  in  all  probability  a  syncytial 
lining  (Kupffer)  consisting  of  thin  continuous  lamellae,  the  proto- 
plasm appearing  as  a  network  of  threads,  with  nucleated  masses 
of  protoplasm  at  nodal  points  of  this  network.  In  places  where 
this  protoplasm  is  present  in  larger  quantity  and  contains  round  or 


296  THE    DIGESTIVE    ORGANS. 

oval  nuclei  it  is  more  readily  brought  out  with  special  stains,  and 
appears  in  such  preparations  in  the  form  of  structures  to  which  the 
name  stellate  cells  has  been  given.  In  such  cells  blood  corpuscles 
and  fragments  of  such  were  often  found.  The  endothelium  of  these 
capillaries  possesses,  therefore,  a  phagocytic  function,  taking  up  par- 
ticles of  foreign  matter,  blood-corpuscles,  etc. 

The  efferent  ducts  of  the  liver,  the  bile-ducts,  are  lined  by  col- 
umnar epithelium,  varying  in  height  in  direct  proportion  to  the  cal- 
iber of  the  passage.  The  smallest  ducts  possess  a  low,  the  medium 
sized  a  cubical,  and  the  larger  a  columnar  epithelium.  The  smaller 
bile-ducts  have  no  clearly  defined  external  walls  other  than  the 
membrana  propria  ;  the  larger  ones,  on  the  other  hand,  possess  a 
connective-tissue  sheath  which  may  even  present  two  layers  in  the 
larger    passages.       Unstriped  muscular  fibers   occur  in  the   large 


Fig.  237. — From  preparation  from  the  liver  of  a  rabbit,  showing  the  so-called  stellate 
cells  of  Kupffer  :  a.  Stellate  cells;  b,  liver  cells. 


ducts,  and  also  small  mucous  glands.  The  gall-bladder  consists 
of  a  mucous,  fibro-muscular,  and,  where  covered  by  the  peritoneum, 
of  a  subserous  and  serous  coats,  as  has  recently  been  shown 
by  Sudler,  whose  account  is  here  followed. 

The  mucous  coat  is  covered  by  a  .single  layer  of  columnar  epi- 
thelium, with  nuclei  situated  in  the  basal  portions  of  the  cells.  The 
epithelial  cells  rest  on  a  poorly  developed  muscularis  mucosae.  The 
mucosa  presents  folds,  covering  ridges  of  connective  tissue  of  the 
fibro-muscular  layer,  and  contains  small  lymph-nodules,  and  a 
varying  number  of  small  mucous  glands.  The  fibro-muscular 
layer  consists  of  interlacing  bands  of  nonstriated  muscle  and 
fibrous  connective  tissue,  and  is  not  arranged  in  distinct  layers. 
The  subserous  and  serous  coats  present  the  same  appearance  as  in 
other  regions  of  the  peritoneum.  The  artery  or  arteries  going  to 
the  gall-bladder  divide  into  branches  which  form  capillaries  in  the 
mucosa   under  the   epithelium ;    these   are   most  numerous  in  the 


THE    LIVER. 


297 


folds  above  mentioned.  The  lymphatics  form  a  subserous  and 
submucous  plexus. 

The  lymphatics  accompany  the  portal  vein  and  hepatic  artery, 
also  the  branches  of  the  hepatic  vein  (Wittich).  They  form  a  net- 
work in  the  interlobular  connective  tissue.  The  lymphatics  form 
further  a  superficial  network  in  subserous  layer  of  the  peritoneum. 
The  superficial  lymphatics  and  the  lymphatics  accompanying  the 
vessels  are  in  communication. 

Within  the  lobules,  the  lymphatics  occur  as  perivascular  spaces, 
as  was  first  shown  by  MacGillavry.  F.  P.  Mall,  who  has  recently 
studied  the  origin  of  the  lymphatics  in  the  liver,  summarizes  his 
results  as  follows  :  The  lymphatics  of  the  liver  arise  from  peri- 
lobular lymph-spaces,  and  these  communicate  directly  with  peri- 
vascular lymph-spaces ;  the  lymph  reaches  these  spaces  by  a  process 
of  filtration  through  openings  which  are  normally  present  in  the 
capillary  walls  of  the  liver. 


^   T  *       H     ^l^.    —Interlobular 


con- 
nective tissue. 


Stellate  cells. 


Fie.  238. —Part  of  a  section  through  liver  lobule  from  dog,  showing  stellate  cells; 

X168. 

Berkley  (94)  has  described  several  divisions  of  the  intrinsic  nerves 
of  the  liver,  all  connected  and  morphologically  alike.  These  nerves 
are  no  doubt  the  neuraxes  of  sympathetic  neurones,  the  cell-bodies 
of  which  are  located  in  ganglia  outside  of  this  organ.  No  medul- 
lated  fibers  were  found  by  him,  although  it  seems  probable  that  the 
nerve-fibrils  terminating  between  the  cells  of  the  bile-ducts  (see  be- 
low) are  terminal  branches  of  sensory  nerve-fibers.  The  nerves  of 
the  liver  accompany  the  portal  vessels,  the  hepatic  arteries,  and  the 
bile-ducts.  The  first  division  of  the  nerves,  embracing  the  larger 
number  of  the  intrinsic  hepatic  nerves,  accompany  the  branches 
of  the  portal  vessels,  form  plexuses  about  them,  and  end  in  inter- 
lobular and  intralobular  ramifications,  the  latter  showing  here  and 
there  knob-like  terminations  on  the  liver-cells,  and,  in  their  course, 
give  off  here  and  there  branches  which  end  on  the  portal  vessels. 


298  THE    DIGESTIVE    ORGANS. 

The  nerve-fibers  following  the  hepatic  arteries  are  in  every  respect  like 
the  vascular  nerves  in  other  glands.  Some  of  the  terminal  branches 
seem,  however,  to  end  on  hepatic  cells.  The  nerve-fibers  following 
the  bile-ducts  may  be  traced  to  the  smaller  and  medium-sized 
ducts,  forming  a  network  about  them,  and  ending  here  and  there 
in  small  twigs  on  the  outer  surface  of  the  cells,  and  occasionally, 
it  would  seem,  between  the  epithelial  cells  lining  the  ducts.  The 
suggestion  seems  warranted  that  these  terminal  fibrils  are  the  end- 
ings of  sensory  nerves.  Some  of  the  nerve-fibers  following  the 
bile-ducts  may  be  traced  into  the  hepatic  lobules.  The  intralobu- 
lar plexus  is  formed,  therefore,  by  the  terminal  branches  of  the  non- 
medullated  nerve-fibers  accompanying  the  portal  and  hepatic  ves- 
sels and  the  bile-ducts.  In  the  wall  of  the  gall-bladder  are  found 
numerous  small  sympathetic  ganglia  formed  by  the  grouping  of  the 
cell-bodies  of  sympathetic  neurones  (Dogiel).  The  neuraxes  of  these 
innervate  the  nonstriated  muscle  of  this  structure.  Large,  medul- 
lated  nerve-fibers  may  be  traced  through  these  ganglia  which 
appear  to  end  in  free  sensory  endings  in  and  under  the  epithelium 
lining  the  gall-bladder  (Huber). 

In  the  human  embryo  the  liver  originates  from  the  intestine 
during  the  second  month  as  a  double  ventral  diverticulum.  Later 
solid  trabecular  masses  are  developed  which  then  unite  and  become 
hollow.  At  this  stage  the  whole  gland  is  uniform  in  structure,  as 
a  division  into  lobules  does  not  take  place  until  later.  The  bile 
capillaries  are  surrounded  by  more  than  two  rows  of  cells.  In  this 
stage  the  embryonal  liver  suggests  a  condition  which  is  permanent 
during  the  life  of  certain  animals.  Only  later  when  the  venae  ad- 
vehentes,  which  later  represent  the  branches  of  the  portal  vein, 
penetrate  the  liver,  is  there  a  secondary  division  into  lobules  (about 
the  fourth  month),  by  which  process  the  primitive  type  gradually 
chang-es  to  that  characteristic  of  the  adult. 


E.  THE  PANCREAS. 

Like  the  liver,  the  pancreas  is  an  accessory  intestinal  gland,  and 
originates  as  a  diverticulum  of  the  intestine.  It  remains  in  perma- 
nent communication  with  the  intestine  by  means  of  its  duct — the 
pancreatic  or  Wirsungian  duct.  The  pancreas  is  composed  of 
numerous  microscopic  lobules,  surrounded  by  connective  tissue 
which  penetrates  into  the  lobules  and  between  the  alveoli  and 
is  accompanied  by  vessels  and  nerves.  The  secretory  portion 
of  the  organ  may  be  regarded  as  a  compound,  branched  alveo- 
lar gland,  the  general  structure  of  which  is  shown  in  Fig. 
240,  the  alveoli  forming  the  principal  portion  of  the  gland. 
The  epithelial  walls  of  the  alveoli  consist  of  a  number  of 
secretory  cells,  whose  appearance  varies  according  to  the  func- 
tional state  of  the  organ.      The  basilar  portions  of  the  cells  present 


THE    PANCREAS. 


299 


a  homogeneous  protoplasm,  while  those  parts  of  the  cells  border- 
ing upon  the  lumen  are  granular.     The  relation  of  these  zones  to 


Nucleus  and 
outer  zone. 


Fig.  239. — Transverse  section  through  alveolus  of  frog's  pancreas. 

each  other  depends  upon  the  physiologic  condition  of  the  gland ; 
during  starvation  the  internal  or  granular  zone  is  wide  and  promi- 
nent ;  after  moderate  secretion  the  cells  become  as  a  whole  some- 
what smaller,  the  granules  decrease  in  number,  and  the  outer  or 
protoplasmic  zone  increases  in  size.  After  prolonged  secretion 
there  is  an  entire  absence  of  the  granules,  and  the  whole  cell  appar- 
ently consists  of  homogeneous  protoplasm.    It  is  therefore  probable 


Fig.   240. — Model  of  lobule  of  human  pancreas    (Maziarski,    "Anatomische  Hefte," 

1901). 

that  during  a  state  of  rest  peculiar  granules  (zymogen  granules)  are 
formed  at  the  expense  of  the  protoplasm,  and  that  these  granules 
represent  a  preliminary  stage  of  the  finished  secretion.      During  the 


300 


THE    DIGESTIVE    ORGANS. 


functional  activity  of  the  gland  the  granules  gradually  disappear, 
while  the  fluid  secretion  simultaneously  makes  its  appearance  in  thc> 
lumen,  although  the  granules  have  as  yet  never  been  observed  in 
the  lumen  itself  After  secretion  the  cell  grows  again  until  it 
reaches  its  original  size,  only  again  to  begin  the  formation  of  zymo- 
gen granules.  Whether  the  cells  of  the  gland  are  destroyed  or  not 
during  secretion  is  still  a  matter  of  uncertainty,  but  does  not  seem 
probable. 

An  intermediate  tubule  similar  to  those  of  the  salivary  glands 
connects  with  each  alveolus,  and  then  passes  over  into  a  short  in- 
tralobular duct.  This  is  lined,  as  in  the  salivary  glands,  with 
columnar  epithelial  cells,  which  are  not,  however  (at  least  in 
man),  -striated  at  their  basal  ends.     The  intralobular  ducts  merge 


Centro-acinal 
cell. 


Intermediary 
duct. 


Intralobular  _ 
duct. 


Alveolus. 


_  Intermediary 
duct. 


Fig.  241. — From  section  through  human  pancreas  ;   X  about  200  (subHmate). 


into  excretory  ducts,  which  finally  empty  into  the  pancreatic  duct. 
The  epithelium  of  the  excretory  ducts  is  simple  columnar  in  type. 
Goblet  cells  are  seen  only  in  the  pancreatic  duct. 

In  the  secreting  alveoli  small  protoplasmic,  polygonal,  and  even 
stellate  cells  are  often  seen,  the  so-called  centro-acinal  cells,  or  cells 
of  Langerhans.  The  significance  of  these  structures  is  not  fully 
understood.  Langerhans  himself  supposed  that  they  belonged  to 
the  walls  of  the  excretory  ducts.  This  interpretation  seems  war- 
ranted by  the  fact  that  it  has  been  found  that  the  secreting  cells  of 
the  alveoli  are  directly  joined  to  the  low  cells  of  the  intermediate 
tubules.  When  the  alveoli  lie  closely  packed  together,  the  ad- 
joining intermediate  tubules  fuse  and  are  reduced  to  one  or,  at 
most,  a  few  cells.  As  a  result  a  condition  is  seen  within  the 
alveolar  complexus,  especially  when  the  excretory  ducts  are  in  a 
collapsed  state,  closely  resembling  the  structures  seen  by  Langer- 


THE    PANCREAS. 


301 


hans.  Peculiar  cells,  wedged  in  here  and  there  between  the  secre- 
tory cells,  but  resting  on  the  membrana  propria,  have  also  been 
observed.  They  undoubtedly  are  sustentacular  cells  of  the  gland 
(cuneate  cells,  Podwyssotzki,  82). 

The  mcuibrana  pi'opria  of  the  alveoli  is  probably  homogenous. 
Immediately  adjoining  it  is  another  delicate  but  firm  membrane, 
consisting  of  fibrils  whose  structure  in  many  respects  resembles  that 
of  the  reticular  fibers  (Gitterfasern)  in  the  liver  and  spleen,  but  which 
are  here  in  relation  to  the  alveoli  (Podwyssotzki,  82). 

In  warm-  and  cold-blooded  animals,  groups  of  cells  differing  in 
arrangement,  size,  and  structure  from  the  secretory  cells,  are  found 
among  the  gland  tubules  and  alveoH  of  the  pancreas  ;  these  are 
known  as  the  intertiibular  cell-masses,  or  areas  of  Langerhans.  They 
are  most  numerous  in  the  splenic  end  of  the  pancreas  (Opie).     They 


Outer  zone  of  — . 
a  secretory  £ 
cell. 


Connective  — 
tissue. 


Larger  gland  — 
duct. 


Centro-acinal 
cell. 


Centro-acinal 
cell. 


Iriiermediate 

tubule. 
Inner  granular 

zone  of  secre- 

tory  cells. 


Fig.   242. — From  section  through  human  pancreas  ;  X  45°  (sublimate) 


consist  of  slightly  granular  cells,  smaller  than  the  secretory  cells 
of  the  alveoli,  arranged  in  the  form  of  anastomosing  trabeculae,  with 
irregular  spaces,  varying  in  size,  separating  the  trabeculae.  Dogiel 
(93)  has  shown  that  in  a  well-preserved  human  pancreas  treated 
by  the  chrome-silver  method,  in  which  the  gland  ducts  even  to 
their  finest  intra-alveolar  branches  were  well  stained,  no  ducts  were 
found  in  the  areas  of  Langerhans.  Such  areas  are,  in  the  human 
pancreas,  usually  separated  from  the  surrounding  gland  tissue  by  a 
small  amount  of  connective  tissue.  They  possess  a  blood  supply, 
consisting  of  relatively  large  capillaries  found  in  the  spaces  formed 
by  the  trabecular  of  cells  above  mentioned.  The  areas  of  Langer- 
hans have  been  variously  interpreted.  The}'  have  been  looked 
upon  as  small  areas  of  gland  tissue  in  process  of  degeneration,  or 


302 


THE    DIGESTIVE    ORGANS. 


again  as  areas  of  embryonic  gland  tissue.  From  their  structure 
and  distinct  blood  supply,  and  the  fact  that  no  ducts  have  been 
traced  into  these  areas,  it  seems  probable  that  they  are  small  masses 
of  cells  forming  a  secretion  which  passes  into  the  blood-vessels — in- 
ternal secretion. 

The  blood-vessels  after  entering  the  gland,  divide  into  smaller 
branches  in  the  lobules,  and  finally  break  up  into  capillaries  which 


Centro-acinal 
cell. 


Secretory  cell. 


Intermediate 
duct. 


Fig.  243. — Scheme  showing  relation  of  three  adjoining  alveoli  to  excretory  duct, 
illustrating  origin  of  centro-acinal  cells. 


^'^o        /if-» 


Blood  capillary. 


Alveolus  or  gland. 


Area  of  Langer- 
hans. 


Fig.  244. — From  section  of  human  pancreas,  showing  gland  alveoli  surrounding  an  area 

of  Langerhans. 

encircle  the  secreting  alveoli.  The  blood-vessels  do  not  follow  the 
course  of  the  ducts  so  regularly  as  in  the  salivary  glands  (Flint). 
The  meshes  of  the  capillary  network  are  not  all  of  the  same  size. 
In  some  regions  they  are  so  wide  that  quite  large  areas  of  the 
alveoli  are  without  blood-vessels. 

The  nerves  of  the  pancreas  have  been  investigated  by  CajaJ  and 
Sala  (91)  and  Erik  Müller  (92),  who  find  in  this  gland  large  num- 
bers of  nonmedullated  nerve-fibers,  some  coming  from  sympathetic 


TECHNIC.  303 

ganglion  cells  situated  in  the  pancreas  and  others  entering  from 
without.  The  nonmedullated  nerve-fibers  form  plexuses  surround- 
ino-  the  excretory  ducts  and  end  in  periacinal  networks.  Fibrils 
from  the  network  about  the  alveoli  were  traced  to  the  secretory 
cells.  A  portion  of  the  nonmedullated  nerves  in  the  pancreas  form 
perivascular  plexuses.  _ 

The  development  of  the  pancreas  is  peculiar  m  that  the  larger 
portion  together  with  the  duct  of  Santorini,  originates  from  the 
dorsal  'intestinal  wall,  and  a  smaller  portion  from  the  ductus  chole- 
dochus  The  latter  part,  with  its  accessory  pancreatic  duct,  fuses 
with  the  former,  after  which  there  is  a  gradual  retrogression  of  the 
duct  of  Santorini,  so  that  finally  the  entire  secretion  of  the  pancreas 
almost  invariably  flows  into  the  pancreatic  or  Wirsungian  duct. 

TECHNIC. 

The  oral  mucous  membrane  may  be  fixed  with  corrosive  sublimate  or 
alcohol,  stained  in  bulk,  and  examined  in  cross- section.  If  special 
structures,  such  as  glands,  nerves,  or  the  distribution  of  mitoses,  are  to  be 
examined,  special  methods  must  be  adopted. 

Teeth.— In  order  to  obtain  a  general  view  of  the  structure  of  the 
teeth,  the  latter  must  be  macerated  and  ground  as  in  the  case  of  bone. 

The  relations  of  the  hard  and  soft  parts  in  undecalcified  teeth  are 
best  studied  by  the  use  of  Koch's  petrifaction  method. 

The  teeth  may  also  be  examined  in  section,  and  when  decalcified  are 
treated  as  bone.  Hydrochloric  acid,  dilute  chromic  acid,  and  picric  acid 
dissolve  the  enamel  prisms,  their  cement-substance  being  the  first  to 
disappear  (von  Ebner,  91). 

The  enamel  of  young  teeth  stains  brown  in  a  solution  of  chromic  acid 
or  its  salts,  and  blackens  in  osmicacid.  In  the  enamel  cells,  globules  are 
seen,  which  are  stained  in  osmic  acid.  If  longitudinal  sections  of  the 
enamel  be  corroded  with  hydrochloric  acid,  the  cruciform  arrangement 
of  the  enamel  prisms  is  plainly  seen. 

The  fibrils  of  the  dentin  may  be  demonstrated  by  decalcifying  a  tooth 
in  the  fluid  recommended  by  von  Ebner,  the  teeth  of  young  individuals 
being  well  adapted  for  this  purpose.  Occasionally  carious  teeth  also 
show  the  fibrils  plainly.  Corrosion  with  hydrochloric  acid  produces  the 
same  result. 

The  cementum,  especially  that  part  lacking  in  cells,  contains  a  large 
number  of  Sharpey's  fibers. 

The  development  of  the  teeth  is  studied  in  the  embryo  ;  the  jaw-bone 
is  fixed,  decalcified,  and  cut  in  serial  sections.  The  most  convenient 
material  is  a  sheep  embryo,  which  can  almost  always  be  had  from  the 
slaughter-house. 

Taste=buds.— To  study  the  taste-buds  of  the  tongue  and  the  rela- 
tions which  their  constituent  cells  bear  to  each  other,  fixation  in  Flem- 
ming's  fluid  is  recommended.  The  orientation  of  the  taste-buds  must  be 
very  carefully  done,  after  which  exactly  longitudinal  or  transverse  serial 
sections  are  made  (not  thicker  than  5  /i)  and  stained  with  safranin- 
gentian-violet. 


304  THE    DIGESTIVE    ORGANS. 

The  nerves  in  the  taste-buds  are  brought  out  either  by  Golgi's 
method,  the  methylene-blue  method,  or  by  the  use  of  gold  chlorid.  If 
the  last  be  used  the  procedure  is  as  follows  :  A  papilla  foliata  of  a  rabbit 
is  removed  with  a  sharp  razor  and  placed  for  ten  minutes  in  lemon  juice, 
then  in  gold  chlorid  for  from  three-quarters  of  an  hour  to  one  hour,  after 
which  the  specimen  is  placed  in  water  weakly  acidulated  with  acetic  acid 
(5  drops  to  100  c.c.  of  water)  and  exposed  to  the  light.  As  soon  as 
reduction  has  taken  place  the  specimen  is  treated  with  alcohol  and  cut  in 
vertical  sections.  These  may  be  treated  for  a  short  time  with  formic 
acid  (in  which  they  swell  slightly),  washed  with  water,  and  mounted  in 
glycerin. 

In  certain  objects,  such  as  the  nictitating  membrane  of  the  frog, 
certain  lobules  of  the  rabbit's  pancreas  (the  latter  being  so  thin  as  to  be 
especially  well  adapted  for  microscopic  examination),  etc.,  the  glandular 
structure  may  be  examined  in  normal  salt  solution. 

Glands  of  the  Digestive  Tract. — Microscopically,  the  glands  pre- 
sent varying  pictures  according  to  the  phase  of  secretion  in  which  they 
are  fixed.  Specimens  in  the  different  stages  may  be  obtained  either  by 
feeding  and  then  killing  the  animal  after  a  definite  period,  or  by  irritating 
certain  nerves,  or  finally  by  the  use  of  certain  poisons  especially  adapted 
to  this  purpose,  such  as  atropin  and  pilocarpin.  In  the  rabbit,  for  in- 
stance, I  c.c.  of  a  5^  solution  of  pilocarpin  hydrochlorate  or  i  c.c.  of 
a  0.5^  solution  of  atropin  sulphate  is  used  for  each  kilogram  of  the  ani- 
mal's weight.  In  atropin- intoxication  secretion  is  suppressed,  while  in 
pilocarpin-poisoning  it  is  increased.  By  this  method  cells  are  obtained 
either  full  of  secretion  or  containing  no  secretion  at  all. 

Sections  should  be  made  from  carefully  selected  material 
which  has  been  fixed  either  in  Flemming's  solution  or  corrosive  subli- 
mate, although  fixation  with  strong  alcohol  also  gives  instructive  pictures. 

In  preparations  fixed  with  Flemming's  solution  the  crescents  of 
Gianuzzi  stain  somewhat  more  deeply  than  the  remaining  cells  of  the 
alveoli,  and  in  objects  that  have  been  treated  with  alcohol  or  corrosive 
sublimate  and  then  stained  with  hematoxylin  the  crescents  take  on  a  very 
deep  color.  The  intermediate  tubules  of  the  salivary  glands  also  assume 
a  deeper  stain  with  hematoxylin  and  carmin.  The  intralobular  tubes  are 
particularly  well  defined  by  certain  stains,  as  for  instance  when  Congo  red 
is  used  after  staining  with  hematoxylin  ;  other  acid  anilin  stains  may 
also  be  used.  The  intralobular  tubes  of  most  salivary  glands  (not,  how- 
ever, of  the  parotid  of  the  rabbit  nor  of  the  sublingual  of  the  dog)  are 
stained  a  dark -brown  color  (calcareous  reaction)  by  agitating  small, 
fresh  pieces  of  tissue  in  order  to  facilitate  the  entrance  of  air,  and 
then  treating  them  with  a  dilute  aqueous  solution  of  pyrogallic  acid. 
The  stain  persists  for  some  time  in  specimens  preserved  in  alcohol.  Sec- 
tions made  by  free  hand  from  tissues  treated  by  this  method  give  excel- 
lent results. 

Mucin  is  soluble  in  dilute  alkalies,  as  for  instance  lime-water, 
and  may  be  precipitated  from  these  solutions  by  the  addition  of  acetic 
acid,  although  the  precipitate  does  not  redissolve  in  an  excess  of  acetic 
acid  ;  mucin  is  also  precipitated  by  alcohol,  but  not  by  heat.  Mucin- 
ogen  does  not  stain  with  hematoxylin,  as  does  mucin.  By  this  latter  test 
a  gland  in  a  state  of  functional  activity  may  be  differentiated  from  one 
at  rest    (R.  Heidenhain,   83).     After  treatment  with  alcohol,   safranin 


TECHNIC.  305 

Stains  mucin  orange-yellow.  For  the  demonstration  of  mucin,  more  es- 
pecially in  alcoholic  preparations,  H.  Hoyer  (90)  has  recommended 
thionin  or  its  substitute,  toluidin-blue.  Indeed,  the  basic  anilin  dyes  in 
general  seem  to  have  a  particular  affinity  for  mucin. 

P.  Mayer  (96)  recommends  the  following  two  solutions  for 
the  staining  of  mucin:  (i)  Mucicarmin — Carmin  i  gm.,  aluminium 
Chlorid  0.5  gm.,  and  distilled  water  2  c.c.  are  stirred  together  and 
heated  over  a  small  flame  till  the  mixture  becomes  quite  dark.  As  soon 
as  the  mixture  has  attained  the  consistency  of  thick  syrup,  50%  alcohol 
is  added  and  the  whole  transferred  to  a  bottle  in  which  it  is  shaken  after 
the  addition  of  more  alcohol.  Finally,  still  more  50%  alcohol  is  added 
until  the  whole  amounts  to  100  c.c.  Before  using,  this  stock  solution  is 
diluted  tenfold  with  tap-water  rich  in  lime-salts.  (2)  Muchematein  : 
(a)  Aqueous  solution — 0.2  gm.  of  hematein  is  ground  in  a  mortar  con- 
taining a  few  drops  of  glycerin;  to  this  are  added  o.i  gm.  aluminium 
Chlorid,  40  c.c.  glycerin,  and  60  c.c.  distilled  water.  (^)  Alcoholic 
solution — 0.2  gm.  hematein,  o.i  gm.  aluminium  chlorid,  100  c.c.  70^0 
alcohol,  and  i  or  2  drops  of  nitric  acid.  Both  of  these  solutions  are  used 
for  staining  mucin  in  sections  and  thin  membranes.  By  the  use  of  these 
methods  the  mucous  acini  of  mixed  glands  are  shown  with  ease  and  pre- 
cision. Under  favorable  conditions  the  whole  secretory  and  excretory 
system  of  the  gland  may  be  brought  out  by  Golgi's  method  (see  this). 

In  order  to  obtain  a  general  structural  view  of  the  esophagus  a 
small  animal  may  be  selected,  in  which  case  small  pieces  of  tissue  are 
fixed  and  imbedded  in  paraffin.  If  a  large  animal  is  used,  the  tissue  is 
imbedded  in  celloidin. 

The  mucous  membrane  of  the  stomach  should  be  fixed  while 
still  fresh  and  warm,  the  best  fixative  for  this  purpose  being  corrosive  sub- 
limate. Mixtures  of  osmic  acid  are  also  serviceable,  but  fixing  with  cor- 
rosive sublimate  increases  the  staining  power  of  the  tissue.  In  order  to 
preserve  the  stomach  and  intestine  in  a  dilated  condition,  they  should  be 
filled  with  the  fixing  fluid  and  after  ligation  placed  whole  in  the  fixing  agent. 
In  gastric  mucous  membrane  that  has  been  fixed  either  with  corrosive 
sublimate  or  alcohol,  the  parietal  cells  are  easily  diff"erentiated  from  the 
chief  cells  by  staining.  The  most  reliable  and  convenient  method  is  as 
follows:  Sections  fastened  to  the  slide  by  the  water-albumin  fixative 
method  are  stained  with  hematoxylin  and  then  placed  in  a  dilute 
aqueous  solution  of  Congo  red  until  they  assume  a  red  color  (minutes); 
they  are  then  washed  with  dilute  alcohol  until  the  parietal  cells  appear 
red  and  the  chief  cells  bluish  (Stintzing).  Almost  all  acid  anilin  dyes 
have  an  affinity  for  the  parietal  cells  ;  hence  the  red  stains  may  be  com- 
bined with  hematoxylin  and  the  blue  ones  with  carmin.  The  chief  cells 
then  take  the  color  of  the  carmin  or  hematoxylin,  and  the  parietal  cells 
that  of  the  anilins. 

An  accurate  fixation  of  that  portion  of  the  small  intestine  possessing 
villi  is  attended  with  great  difficulty,  since  the  axial  tissue  of  the  villi 
shows  a  tendency  to  retract  from  the  epithelial  layer  surrounding  it 
(the  latter  becoming  fixed  first);  and  as  a  consequence  spaces  are  formed 
at  the  summits  of  the  villi  which  undoubtedly  represent  artefacts.  A 
good  method  is  to  cut  pieces  from  tissue  while  still  warm  and  fix  in  osmic 
acid.  If  portions  of  the  intestine  be  filled  with  alcohol  or  corrosive  sub- 
limate and  thus  dilated,  both  the  glands  and  villi  are  shortened.     The 


306  THE    DIGESTIVE    ORGANS. 

methods  above  mentioned  for  staining  mucin  may  be  used  to  stain  the 
goblet  cells.  The  villi  may  also  be  examined  in  a  fresh  condition  in  one 
of  the  indifferent  fluids.  For  this  purpose  the  intestine  of  the  mouse  is 
especially  well  adapted. 

The  absorption  of  fat  is  best  studied  in  preparations  fixed  in  osmic 
acid,  and  especially  in  those  treated  by  Altmann 's  method. 

The  technic  for  the  solitary  lymph-follicles  and  Peyer's  patches 
is  the  same  as  that  for  lymph-glands.  For  this  purpose  the  cecum  of  a 
rabbit  or  guinea-pig  is  the  best  material. 

The  nerves  of  the  intestinal  mucous  membrane  are  best  demon- 
strated by  means  of  the  methylene -blue  method  or  Golgi's  method  {yid. 
Technic),  and  the  coarser  filaments  of  Auerbach' sand  Meissner' s  plexuses 
may  also  be  stained  by  the  gold  method  (Lö wit's  procedure,  p.  48). 
Good  results  are  also  obtained  by  staining  with  hematoxylin  such  speci- 
mens as  have  been  previously  fixed  and  distended  with  alcohol.  The 
plexuses  then  appear  somewhat  darker  than  the  remaining  tissue  of  the 
isolated  mucous  membrane  or  muscular  layer. 

Liver. — The  arrangement  of  the  liver  lobules  is  best  seen  in  the  pig's 
liver.  In  the  human  liver  and  in  most  domestic  animals  the  lobules  are 
not  sharply  defined,  two  or  three  adjacent  lobules  merging  into  each 
other.  In  the  liver  of  the  fetus,  of  the  new-born,  and  of  children,  the 
lobules  are  seen  indistinctly  or  not  at  all,  although  the  perivascular  spaces 
of  the  blood-vessels  are  better  seen  than  in  the  adult. 

The  liver-cells  are  best  examined  by  treating  small  pieces  of  tissue 
with  I  ^  osmic  acid  or  osmic  mixtures  ;  in  the  latter  case  subsequent 
treatment  with  pyroligneous  acid  is  necessary.  Good  results  can  also  be 
obtained  by  fixing  with  corrosive  sublimate  and  staining  with  hematoxylin 
(after  M.  Heidenhain). 

In  order  to  see  the  glycogen  in  the  liver-cells  Ranvier  (89)  proceeds 
as  follows  :  A  dog  is  fed  on  boiled  potatoes  for  two  days,  after  which 
sections  of  its  liver  are  cut  with  a  freezing  microtome  and  examined  in 
iodized  serum.  In  a  short  time  the  glycogen  is  stained  a  wine-red.  If 
the  preparation  be  now  exposed  to  osmic  acid  vapor,  the  stain  will  remain 
fixed  for  from  twenty-four  to  forty-eight  hours.  Glycogen  is  insoluble  in 
alcohol  and  ether,  and  stains  a  port  wine-red  in  iodin  solutions  ;  the 
color  disappears  when  the  specimen  is  warmed,  but  returns  again  on  cool- 
ing. 

The  distribution  of  the  hepatic  blood-vessels  is  usually  demon- 
strated by  injection  of  the  portal  vein,  as  the  injection  of  the  hepatic 
artery  does  not,  as  a  rule,  give  such  satisfactory  results. 

The  injection  method  is  also  employed  for  the  demonstration 
of  the  bile  capillaries.  Chrzonszczewsky  recommends  the  following 
so-called  physiologic  autoinjection  :  A  saturated  aqueous  solution  of 
indigo-carmin  is  injected  into  the  external  jugular  vein  three  times  in  the 
course  of  one  and  one-half  hours  (dog  50  c.c.  each  time,  cat  30  c.c, 
full-grown  rabbit  20  c.c).  The  animal  is  then  killed  and  small  pieces 
of  its  liver  fixed  in  absolute  alcohol  or  in  potassium  chlorate ;  in  the  latter 
case  a  saturated  solution  of  the  salt  may  be  injected  into  the  blood-ves- 
sels. A  subsequent  injection  of  the  blood-vessels  with  carmin -gelatin 
ttiay  also  be  employed,  and  the  whole  liver  then  hardened  in  alcohol.    By 


TECHNIC.  307 

this  method  the  bile  capillaries  finally  become  filled  with  the  indigo-car- 
min  by  a  gradual  elimination  of  the  substance  from  the  blood-  and  lymph- 
vessels  and  passage  through  the  cells  into  the  biliary  system,  while  the 
blood-vessels  themselves  are  distended  by  the  carmin-gelatin.  In  the 
frog,  the  demonstration  of  the  biliary  passages  is  more  easily  accomplished 
by  injecting  2  c.c.  of  the  indigo-carmin  solution  into  the  large  lymph- 
sac  and  killing  it  after  a  few  hours.  The  liver  is  then  fixed  in  the  manner 
described  above  and  is  then  ready  for  further  treatment. 

The  bile  passages  may  also  be  injected  directly  through  the 
hepatic  duct  or  the  ductus  choledochus.  For  this  purpose  it  is  best  to 
use  a  concentrated  aqueous  solution  of  Berlin  blue  (Berlin  blue  that  is 
soluble  in  water).  The  results  obtained  by  this  method  are  not,  however, 
always  satisfactory,  and  even  in  the  best  of  cases  only  the  peripheral  por- 
tions of  the  liver  lobules  are  successfully  injected. 

The  bile  capillaries  may  be  impregnated  with  chrome-silver. 
Fresh  pieces  of  liver  tissue  are  placed  for  two  or  three  days  in  a  potas- 
sium bichromate-osmic  acid  solution  (4  vols,  of  a  3%  bichromate  of 
potassium  solution  and  i  vol.  of  i  %  osmic  acid)  and  then  transferred  to 
a  0.75%  aqueous  solution  of  silver  nitrate.  After  rinsing  in  distilled 
water  the  specimens  are  cut  with  a  razor,  the  sections  again  washed  with 
distilled  water,  placed  for  a  short  time  in  absolute  alcohol,  cleared  m 
xylol,  and  finally  preserved  in  hard  Canada  balsam.  Both  celloidm 
and  paraffin  imbedding  are  admissible,  but  either  process  must  be  hurried, 
as  the  preparation  always  suff'ers  under  such  treatment.  In  the  finished 
specimen,  the  bile  capillaries  appear  black  by  direct  light. 

Another  method  which  brings  to  view  more  extensive  areas  of  the 
bile  capillaries  is  as  follows  :  A  piece  of  liver  tissue  from  a  freshly  killed 
animal  is  fixed  in  rapidly  ascending  strengths  of  potassium  bichromate 
solution  (from  z^fc  to  5%).  After  three  weeks  the  specimen  is  placed 
in  a  0.75%  silver  nitrate  solution,  when  after  a  few  days  (very  marked 
after  eight  days)  the  bile  capillaries,  if  examined  in  sections,  will  appear 
black  by  direct  light  (Oppel,  90). 

Sometimes  the  bile  capillaries  are  brought  out  in  preparations 
treated  by  the  method  of  R.  Heidenhain,  although  only  small  areas  are 
colored  and  these  not  constantly.  The  application  of  other  stains,  as  for 
instance  the  method  of  M.  Heidenhain  following  the  gold  chlorid  treat- 
ment, often  results  in  the  staining  of  small  areas  of  bile  capillaries. 

In  all  the  methods  used  for  the  demonstration  of  the  bile  capil- 
laries, whether  physiologic  autoinjection,  direct  injection,  or  impregna- 
tion,'the  secretion  vacuoles  of  the  liver-cells  are  clearly  brought  to  view. 
By  treating  pieces  of  liver  tissue  according  to  the  method  of 
Kupffer  (76)  the  connective  tissue  of  the  liver,  especially  the  reticular 
structure  {Gitterfasern),  is  shown.  Fresh  liver  tissue  is  cut  with  the 
double  knife  and  the  thinnest  sections  placed  for  a  short  time  m  a  0.6% 
sodium  chlorid  solution  or  in  a  0.05%  solution  of  chromic  acid.  From 
this  they  are  transferred  to  a  very  dilute  solution  of  gold  chlorid  (Gerlach) 
(gold chlorid  i  gm.,  hydrochloric  acid  i  c.c,  water  10  liters),  and  kept 
for  one  to  several  days  in  the  dark  until  they  assume  a  reddish  or  violet 
color.  If  the  staining  has  been  satisfactory  (which  is  by  no  means  always  the 
case),   the  reticular  fibers,  and  occasionally  also  the  stellate  cells,  are 


308  THE    DIGESTIVE    ORGANS. 

seen.     Instead  of  the  double  knife  the  freezing  microtome  may  be  used 
and  the  method  continued  as  stated  (Rothe). 

The  reticula?-  fibers  are  seen  under  more  favorable  conditions  by 
using  the  following  method,  recommended  by  Oppel  (91):  Fresh  pieces 
of  tissue  fixed  in  alcohol  are  placed  for  twenty-four  hours  in  a  0.5^  aque- 
ous solution  of  yellow  Chromate  of  potassium  (larger  pieces  in  stronger 
solutions  up  to  5%),  then  washed  with  a  very  dilute  solution  of  nitrate  of 
silver  (a  few  drops  of  a  0.75^'  solution  to  30  c.c.  distilled  water),  and 
transferred  to  a  0.75^  solution  of  silver  nitrate.  In  twenty-four  hours 
the  intralobular  network  surrounding  the  blood  capillaries  will  have  be- 
come stained.  The  best  areas  lie  at  the  periphery  of  the  specimen,  and 
extend  about  i  mm.  into  the  parenchyma.  Free-hand  sections  are 
made,  or  the  specimens  are  quickly  imbedded  in  celloidin  or  paraffin, 
to  be  cut  afterward  by  means  of  the  microtome.  The  same  results  are 
obtained  by  placing  small  fresh  pieces  of  the  tissue  for  two  or  three  days 
in  a  0.5^  chromic  acid  solution  and  then  one  or  two  days  in  a  0.5^ 
solution  of  silver  nitrate.  The  further  treatment  is  as  in  the  preceding 
method. 

The  method  of  F.  P.  Mall  is  also  employed  in  the  examination  of  the 
hepatic  connective  tissue. 

The  following  method  is  recommended  by  Berkley  for  demon- 
strating the  nerves  of  the  liver  :  Small  pieces  of  liver  tissue  from  0.5  to  i 
mm.  in  breadth  are  placed  in  a  half-saturated  aqueous  solution  of  picric  acid 
for  from  fifteen  to  thirty  minutes,  and  then  in  100  c.c.  of  potassium  bi- 
chromate solution  that  has  been  saturated  in  the  sunlight  and  to  which  16 
c.c.  of  2^  osmic  acid  has  been  added.  The  specimens  now  remain  in 
this  fluid  for  forty-eight  hours  in  a  dark  place,  and  at  a  temperature  of 
25°  C.  After  this  the  tissue  is  treated  with  a  0.25%  to  0.75^  aqueous 
solution  of  silver  nitrate  for  five  or  six  days,  washed  (quick  imbedding 
may  be  employed),  cut,  cleared  in  oil  of  bergamot,  and  mounted  in 
xylol-Canada  balsam. 

The  cellular  elements  of  the  pancreas  may  be  examined  without 
further  manipulation  in  very  thin  lobules  from  the  rabbit  (Kühne  and  Lea). 

There  are  various  methods  of  differentiating  the  inner  and 
outer  zones  of  the  cells.  In  sections  of  the  tissue  fixed  in  alcohol,  car- 
min  stains  the  outer  zone  of  the  cells  more  intensely  than  the  inner  (R. 
Heidenhain,  83).  For  the  staining  of  the  inner  zone,  fixation  in  Flem- 
ming's  fluid  is  to  be  recommended,  then  staining  with  safranin,  and  finally 
washing  in  an  alcoholic  solution  of  picric  acid.  The  granules  of  the 
inner  zone  (zymogen  granules)  appear  red.  These  also  stain  red  with 
the  Biondi-Ehrlich  mixture.  The  simplest  and  most  precise  method  of 
demonstrating  the  zymogen  granules  is  that  of  Altmann.  The  secretory 
and  excretory  ducts  of  the  pancreas  are  shown,  as  in  the  case  of  the 
salivary  glands,  by  the  chrome-silver  method. 


THE    LARYNX. 


309 


IV.  ORGANS  OF  RESPIRATION. 

A.  THE  LARYNX. 

The  greater  portion  of  the  laryngeal  mucous  membrane  is  cov- 
ered by  a  stratified  columnar  ciliated  epithelium  containing  goblet 
cells,  and  resting  on  a  thick  basement  membrane.  The  epithelium 
covering  the  free  margin  of  the  epiglottis,  the  true  vocal  cords,  and 


Glands  in  false 
vocal  cord. 


Stratified  pavement 
epithelium  of  true 
vocal  cord. 


Stratified  ciliated  col- 
umnar epithelium. 


Glands.  __ 


Muscle. 


Muscle. 


Fig.  245. — Vertical  section  through  the  mucous  membrane  of  the  human  larynx  ;  X  5« 


3IO  ORGANS    OF    RESPIRATION. 

part  of  the  arytenoid  cartilage  as  far  as  the  cavity  between  these 
cartilages,  is  of  the  stratified  squamous  variety,  and  is  provided  with 
connective-tissue  ridges  and  papillae.  The  mucosa  consists  of  fi- 
brous connective  tissue,  contains  many  elastic  fibers,  which  become 
larger  and  more  prominent  as  the  deeper  layers  of  the  mucosa  are 
approached,  and  is  rather  firmly  connected  with  the  structures 
underneath  it,  but  is  somewhat  more  loosely  connected  in  the  re- 
gions supplied  with  squamous  epithelium.  The  mucosa  contains 
numerous  lymphocytes  and  leucocytes,  which  now  and  then,  espe- 
cially in  the  region  of  the  ventricles,  form  simple  follicles.  In  it  are 
found  branched  tubulo-alveolar  glands,  which  may  be  single  or 
arranged  in  groups.  These  are  found  at  the  free  posterior  portion 
of  the  epiglottis,  in  the  region  of  the  latter' s  point  of  attachment — 
i.  e.,  in  the  so-called  cushion  of  the  epiglottis.  Larger  collections 
of  glands  are  found  in  the  false  vocal  cords,  and  on  the  cartilages 
of  Wrisberg  (cuneiform  cartilages),  which  appear  almost  imbedded 
in  the  glandular  tissue  and  in  the  ventricles.  In  the  remaining 
parts  of  the  larynx  glands  are  found  only  at  isolated  points.  The 
true  vocal  cords  have  no  glands.  The  glands  of  the  larynx  are 
of  the  mucous  variety,  containing  crescents  of  Gianuzzi. 

The  cartilages  of  the  larynx  are  of  the  hyaline  variety,  with  the 
exception  of  the  epiglottis,  the  cartilages  of  Santorini  (the  latter 
are  derivatives  of  the  epiglottis,  Göppert),  the  cuneiform  cartilages, 
the  processus  vocalis,  and  a  small  portion  of  the  thyroid  at  the 
points  of  attachment  of  the  vocal  cords,  which  consist  of  elastic  car- 
tilage. 

The  vascular  supply  of  the  larynx  is  arranged  in  three  super- 
imposed networks  of  blood-vessels.  The  capillaries  are  very  fine, 
and  lie  directly  beneath  the  epithelium.  The  lymphatic  network  is 
arranged  in  two  layers,  the  superficial  being  very  fine  and  di- 
rectly beneath  the  network  of  blood  capillaries. 

The  nerves  of  the  laryngeal  mucous  membrane  will  be  de- 
scribed in  connection  with  those  found  in  the  trachea. 


B.  THE  TRACHEA. 

The  trachea  is  lined  by  a  stratified  ciliated  columnar  epithelium 
containing  goblet  cells  and  resting  on  a  well-developed  basement 
membrane.  The  mucosa  is  rich  in  elastic  tissue.  In  the  super- 
ficial portion  of  the  mucosa  the  elastic  fibers  form  dense  .strands, 
which  usually  take  a  longitudinal  direction.  The  deeper  layer  of 
the  mucosa  is  more  loosely  constructed,  and  passes  over  into  the 
perichondrium  of  the  semilunar  cartilages  of  the  trachea  without 
any  sharp  line  of  demarcation.  Numerous  leucocytes  are  scattered 
throughout  the  mucosa,  and  are  also  frequently  found  in  the  epi- 
thelium. Connecting  the  free  ends  of  the  semilunar  cartilages, 
which  are  of  the  hyaline  variety,  are  found  bundles  of  nonstriated 
muscle  tissue,  the  direction  of  which  is  nearly  transverse. 


THE  BRONCHI,   THEIR   BRANCHES,   AND  THE  BRONCHIOLES.        3  II 

The  trachea  contains  numerous  branched  tubulo-alveolar  glands 
of  the  mucous  variety  containing  here  and  there  crescents  of 
Gianuzzi.  The  glands  are  especially  numerous  where  the  tracheal 
wall  is  devoid  of  cartilage. 

The  larynx  and  trachea  receive  their  nerve  supply  from  sensory 
nerve-fibers  and  sympathetic  neurones.  These  have  been  described 
by  Ploschko  (97)  working  in  Arnstein's  laboratory.  According  to 
this  observer,  the  sensory  fibers  divide  in  the  mucosa,  forming  sub- 
epithelial plexuses  from  which  fibrils  are  given  off  which  enter  the 
epithelium  of  the  larynx  and  trachea  and,  after  further  division,  end 
on  the  epithelial  cells  in  small  nodules,  or  small  clusters  of  nodules. 
In  the  trachea  of  the  dog,  such  fibrils  were  traced  to  the  ciliary 
border  of  the  columnar  ciliated  cells  before  terminating.  Numerous 
sympathetic  ganglia  are  found  in  the  larynx  and  trachea.  In  the 
latter  they  are  especially  numerous  in  the  posterior  wall.  The 
neuraxes  of  the  sympathetic  neurones  forming  these  ganglia  were 
traced  to  the  nonstriated  muscular  tissue  of  the  trachea.  The  cell- 
bodies  of  these  sympathetic  neurones  are  surrounded  by  end-baskets 
of  small  medullated  fibers  terminating  in  the  ganglia.      Medullated 


Fig.  246. — From  longitudinal  section  of  human  trachea,  stained  in  orcein:   a,  Layer  of 
elastic  fibers  ;   b,  cartilage. 

nerve-fibers,  ending  in  the  musculature  of  the  trachea  in  peculiar 
end-brushes,  were  also  described  by  Ploschko. 


C  THE  BRONCHI,  THEIR  BRANCHES,  AND  THE 
BRONCHIOLES. 

The  primary  bronchi  and  their  branches  show  the  same  general 
structure  as  the  trachea,  showing,  however,  irregular  plates  and 
platelets  of  cartilage  instead  of  half-rings,  which  surround  the 
bronchi.     The  cartilage  is  absent  in  bronchial  twigs  of  less  than 


312 


ORGANS    OF  .RESPIRATION. 


0.85  mm. -in  diameter.  The  epithelium  of  the  bronchi  of  medium 
size  (up  to  0.5  mm.  in  diameter)  consists  of  a  cihated  epithehum 
having  three  strata  of  nuclei.  KöUiker  (81)  distinguishes  a  deep 
layer  of  basilar  cells,  a  middle  layer  of  replacing  cells,  and  a  super- 
ficial zone  consisting  of  ciliated  and  goblet  cells.  The  number 
of  the  last  varies  greatly.  Glands  are  found  only  in  bronchial 
twigs  that  are  not  less  than  i  mm.  in  diameter ;  as  in  the  trachea, 
they  are  branched  tubulo-alveolar  glands  of  the  mucous  variety. 
In  these  structures  the  mucosa  contains  a  large  number  of  elastic 
fibers,  the  greater  part  of  which  have  a  longitudinal  direction. 
Furthermore,  numerous  lymph-cells  are  found,  and  here  and  there 
a  lymph-nodule.  The  muscularis  presents,  as  a  rule,  circular  fibers, 
which  do  not,  however,  form  a  continuous  layer. 

The  smaller  bronchi  subdivide  into  still  finer  tubules  of  less 
than  o.  5  mm.  in  diameter  (bronchioles),  which  contain  neither  car- 


stratified  cili- 

ated  columnaf 

epithelium. 

—  Elastic  fibers, 
cut  trans- 
versely. 


—  Gland. 


Mucosa. 


1^--   Cartilasre. 


««?  " 


,.   Connective 
tissue. 


Fig.  247. — Transverse  section  through  human  bronchus  ;  X  27. 


tilage  nor  glands.  The  stratum  proprium,  as  well  as  the  external 
connective-tissue  sheath,  becomes  very  thin  ;  and  the  epithelium 
now  consists  of  but  one  layer,  but  is  still  ciliated. 


TERMINAL  DIVISIONS  OF  BRONCHI  AND  ULTIMATE  AIR-SPACES.    3  I3 

D,  TERMINAL  DIVISIONS  OF  BRONCHI  AND  ULTIMATE 

AIR-SPACES, 

The  bronchioles  are  continued  as  the   respiratory  bronchioles. 


•^ 


•^-  —  Artery. 


jf    jf-^K-^f        I    _, —  rV-^V^-^-rä--  Lung  tissue. 


,^, Bronchiole. 


,        1    '     .-,V-        i      N   .| 


Respiratorj'    _ 
bronchiole 


S::^fi.-^/U 


"fK"  f-^-'^r  \ife>T  x-^- --„4- 


Alveolar  duct. .^ti,^- X-^'„_1 _l_  f    ''-^i't^',  1    C*-av"*-'^  >^ 

■^  Vl,  / 

vex 


Lung  tissue. 


■?K 


1  '^B,:^""-'  ^ 


Fig.  249. 
Figs.  248  and  249. — Two  sections  of  cat's  lung  :   Fig.  248,  X  5^  ;   Fig.  249,  X  35- 

The  epithelium  of  the  latter  is  ciliated  in  patches,  but  soon  becomes 
nonciliated  and   assumes  the    character   of  respiratory  epithelium. 


3H 


ORGANS    OF    RESPIRATION. 


(See  below.)  The  walls  of  the  respiratory  bronchioles  are  rela- 
tively thin,  consisting  of  fibro-elastic  connective  tissue  and  nonstri- 
ated  muscle.  Our  knowledge  of  the  further  divisions  of  the 
bronchioles  and  of  their  relation  to  the  terminal  air-spaces  has  been 
increased  greatly  by  Miller,  who  has  made  use  of  Born's  method 
of  wax-plate  reconstruction  in  the  study  of  these  structures.  His 
account  is  here  followed.  According  to  Miller,  the  respiratory 
bronchioles  divide  into  or  become  the  terminal  bronchioles  or  alveo- 


Respiratory 
bronchiole. 

Fig.  250. — Internal  surface  of  a  human  respiratory  bronchiole,  treated  with  silver 
nitrate  ;  X  234  (after  KöUiker). 

lar  ducts.  These  are  somewhat  dilated  at  their  distal  ends  and 
communicate,  by  means  of  three  to  six  round  openings,  with  a  cor- 
responding number  of  spherical  cavities,  known  as  atria.  Each 
atrium  communicates  with  a  variable  number  of  somewhat  irregu- 
lar spaces  or  cavities,  the  air-sacs,  the  walls  of  which  are  beset  with 
numerous  somewhat  irregular  hemispheric  bulgings,  the  air-cells 
or  lung  alveoli.  The  air-cells  or  alveoli  are  also  numerous  in  the 
walls  of  the  atria  and  the  terminal  bronchioles  or  alveolar  ducts, 


TERMINAL  DIVISIONS  OF  BRONCHI  AND  ULTIMATE  AIR-SPACES.    3  I  5 

and  may  even  be  found  in  the  walls  of  the  respiratory  bronchioles. 
The  terminal  bronchioles  or  alveolar  ducts  have  an  epithelium 
which  is  of  the  cubic  variety  in  their  proximal  portions,  and  which 
changes  to  a  squamous  epithelium  in  their  distal  portions. 

The  epithelium  of  the  distal  portions  of  the  terminal  bronchi- 
oles or  alveolar  ducts,  atria,  and  air-sacs  (i  i  /^  to  i  5  //  in  diameter) 
and  of  the  alveoli  (the  so-called  respiratory  epitheHum)  consists  of 
two  varieties  of  cells  (F.  E.  Schulze) — smaller  nucleated  elements 
and  larger  nonnucleated  platelets  (the  latter  derived  very  probably 
from  the  former).  The  arrangement  of  the  epithelial  cells  is  gen- 
erally such  that  the  nonnucleated  platelets  rest  directly  upon  the 
blood  capillaries,  while  nucleated  cells  lie  between  them.  In  am- 
phibia the  epithelium  of  the  alveoli  consists  of  cells,  of  which  the 
portion  containing  the  nucleus  forms  a  broad  cylindric  base;  from 


G^j^^^ — ^1 Nonnucleated  epi- 

"       "  thelial  cell. 


1-/    ^^^ Nucleated  epithelial 

fe-    J  cell. 


Fig.  251. — Inner  surface  of  human  alveolus  treated  with  siUer  nitrate,  showing  respira- 
tor} epithelium  ,   X  240  (after  Kolliker). 


the  free  end  of  each  cell  a  lateral  process  extends  over  the  adjoin- 
ing capillary  to  meet  a  similar  process  from  the  neighboring  cell. 
When  viewed  from  above,  the  basal  portion  of  the  cell  appears 
dark  and  granular,  while  the  processes  are  clear  and  transparent. 
These  cells,  together  with  their  prolongations,  are  about  50  p.  in 
diameter.  The  surface  view  greatly  resembles  that  of  the  human 
respiratory  epithelium  (Duval,  Oppel,  89). 

The  terminal  bronchioles  or  alveolar  ducts  have  a  distinct 
layer  of  nonstriated  muscle  having  annular  thickenings  about  the 
openings  which  lead  to  the  atria.  Muscular  tissue  is  not  found  in 
the  walls  of  the  atria,  air-sacs,  and  air-cells  or  alveoli  (Miller). 

Beneath  the  respiratory  epithelium  in  the  atria,  air-sacs,  and  air- 
cells,  there  is  found  a  thin  basement  membrane,  which  is  apparently 
homogeneous.      Here  and  there  are  found   some   fibrils  ot  fibrous 


3i6 


ORGANS    OF    RESPIRATION. 


tissue  and  fixed  connective-tissue  cells.      Elastic  fibers  are,  however, 
numerous,  forming  networks  beneath  the  basement  membrane. 

The  work  of  Miller  has  given  a  clearer  conception  of  what  may 
be  regarded  as  the  units  of  lung  structure,  namely,  the  lobules. 
Such  a  unit  or  lobule  is  composed  of  a  terminal  bronchiole  or 
alveolar  duct,  with  the  air-spaces — atria,  air-sacs,  and  air-cells — 
connected  with  it,  and  their  blood-  and  lymph- vessels  and  nerves. 
The  general  arrangement  of  these  structures  may  be  observed  in 
Fig.  253,  which  gives  a  diagram  of  a  lung  lobule.  The  shape  of  the 
atria,  air-sacs,  and  air-cells  may  be  seen  in  Fig.  254,  which  is  from 
a  wax  reconstruction  of  these  structures. 

The  blood-vessels  of  the  lung,  including  their  relation  to  the 
structures  of  the  lung  lobules,  have  been  investigated  by  Miller;  his 
account  is  closely  followed  in  the  following  description :  The  pul- 
monary artery  follows  closely  the  bronchi  through  their  entire 
length.  An  arterial  branch  enters  each  lobule  of  the  lung  at  its 
apex  in  close  proximity  to  the  terminal  bronchiole.  After  entering 
the  lobule  the  artery  divides  quite  abruptly,  a  branch  going  to  each 
atrium;  from  these  branches  the  small  arterioles  arise  which  supply 
the  alveoli  of  the  lung.  "  On  reaching  the  air-sac  the  artery  breaks  up 
into  small  radicals  which  pass  to  the  central  side  of  the  sac  in  the  sulci 
between  the  air-cells,  and  are  finally  lost  in  the  rich  system  of  capil- 
laries to  which  they  give  rise.  This  network  surrounds  the  whole  air- 
sac  and  communicates  freely  with  that  of  the  surrounding  sacs."  This 
capillary  network  is  exceedingly  fine  and  is  sunken  into  the  epithelium 
of  the  air-sacs  so  that  between  the  epithelium  and  the  capillary  there  is 
only  the  extremely  deHcate  basement  membrane.     Only  one  capillary 

network  is  found  between  any 
two  contiguous  air-cells  or  air- 
sacs.  The  atria,  the  alveolar 
ducts  and  their  alveoli,  and  the 
alveoli  of  the  respiratory  bron- 
chioles are  supplied  with  similar 
capillary  networks.  The  veins 
collecting  the  blood  from  the 
lobules  lie  at  the  periphery  of  the 
lobules  in  the  interlobular  con- 
nective tissue,  and  are  as  far  dis- 
tant from  the  intralobular  arteries 
as  possible.  These  veins  unite  to 
form  the  larger  pulmonary  veins. 
The  bronchi,  both  large  and 
small,  as  well  as  the  bronchioles, 
derive  their  blood  supply  from 
the  bronchial  arteries,  which  also 
partly  supply  the  lung  itself 
Capillaries  derived  from  these  ar- 
teries surround  the  bronchial  system,  their  caliber  varying  according 


Fig.  252. — Scheme  of  the  respiratory 
epithelium  in  amphibia  :  The  upper  figure 
gives  a  surface  view  :  b.  Basilar  portion  ;  a, 
the  thin  process.  The  lower  figure  is  a  sec- 
tion: a,  Respiratory  epithelial  cell ;  b,  blood- 
vessel ;  c,  connective  tissue  around  the  al- 
veoli. 


TERMINAL  DIVISIONS  OF  BRONCHI  AND  ULTIMATE  AIR-SPACES.     3  I  / 


to  the  structure  they  supply— finer  and  more  closely  arranged  in  the 
mucous  membrane,  and  coarser  in  the  connective-tissue  walls.  In 
the  neighborhood  of  the  terminal  bronchial  tubes  the  capillary  nets 
anastomose  freely  with  those  of  the  respiratory  capillary  system. 
From  the  capillaries  of  the  bronchial  arteries,  veins  are  formed  which 
empty  either  into  the  bronchial  veins  or  into  the  branches  of  the 
pulmonary  veins. 


Fig.  253. — Scheme  of  lung  lobule 
after  Miller:  b.  r..  Respiratory  bronchiole  ; 
d.  al.,  alveolar  duct  (terminal  bronchus); 
a,  a,  a,  atria;  s.  al.,  air-sacs;  a.  p.,  air- 
cells  or  alveoli. 


Fig.  254. — Reconstruction  in  wax  of 
a  single  atrium  and  air-sac  with  the  alveoli : 
V,  Surface  where  atrium  was  cut  from  al- 
veolar duct ;  F,  cut  surface,  where  another 
air- sac  was  removed  ;  A,  atrium  ;  S,  air- sac 
with  air-cells  (alveoli)  (after  Miller). 


The  lymphatics  of  the  lung  are  classified  by  Miller  as  follows : 
{a)  lymphatics  of  the  bronchi ;  {b)  lymphatics  of  the  arteries ;  (r) 
lymphatics  of  the  veins;  {d)  lymphatics  of  the  pleura.  The  bron- 
chial lymphatics  are  arranged  in  two  plexuses  as  far  as  cartilage  is 
present  in  the  walls  of  the  bronchi,  one  internal  and  one  external  to 
the  cartilage.  Beyond  the  cartilage  only  a  single  plexus  is  found. 
In  the  terminal  bronchioles  there  are  found  three  lymphatic  vessels, 
two  of  which  pass  to  the  vein  and  one  to  the  artery  of  the  lobules. 
No  lymphatics  are  found  beyond  the  terminal  bronchioles.  The 
larger  arteries  are  accompanied  by  two  lymphatic  vessels;  the 
smaller  ones,  only  one.  The  same  is  true  in  general  of  the  lym- 
phatics accompanying  the  vein.  The  bronchial  lymphatics  and 
those  accompanying  the  arteries  and  veins  anastomose  in  the  regions 
of  the  divisions  of  the  bronchi.  The  pleura  possesses  a  rich  net- 
work of  lymphatics  with  numerous  valves. 

Accompanying  the  bronchi  and  bronchial  arteries  are  found 
numerous  nerve-fibers,  of  the  nonmedullated  and  medullated  varie- 
ties, arranged  in  bundles  of  varying  size,  in  the  course  of  which  are 
found  sympathetic  ganglia.  Berkley  (94),  who  has  studied  the  dis- 
tribution of  the  nerves  of  the  lung  with  the  chrome-silver  method, 
finds  that  in  the  external  fibrous  layer  of  the  bronchi  is  found  a 


3i8 


ORGANS    OF    RESPIRATION. 


plexus  of  very  fine  and  of  coarser  fibers,  from  which  branches  are 
given  off  which  end  in  the  muscle  tissue  of  the  bronchi,  and  others 
which  pass  through  this  layer  to  form,  after  further  division,  a  sub- 


V; 


Fig,  255. — From  section  of  human  lung  stained  in  orcein,  showing  the  elastic  fibers  sur- 
rounding the  alveoli. 


Blood  capillaries 
seen  in  surface 
view. 


^   ^> 


'P^  !\t7*  '  "  r  —  Alveolus  in  cross- 


Fig.  256. — Section  through  injected  lung  of  rabbit. 


epithelial  plexus  from  which  fibrils  may  be  traced  into  the  connec- 
tive-tissue folds  in  the  larger  bronchi  and  between  the  bases  of  the 
epithelial  cells  in  the  smaller  bronchi  and  bronchioles.  Some  few 
fibrils  were  traced  between  alveoli  situated  near  bronchi,  "  termi- 
nating, apparently,  immediately  beneath  the  pavement  epithelium  in 
an  elongated  or  rounded  minute  bulb  ;  "  these  may,  however,  repre- 


THE    THYROID    GLAND. 


319 


sent  endings  on  nonstriated  muscle  tissue.      The  bronchial  arteries 
have  an  exceedingly  rich  nerve  supply. 

The  visceral  and  parietal  layers  of  the  pleura  consist  of  a  layer 
of  fibrous  tissue  containing  numerous  elastic  fibers.  Both  layers  are 
covered  by  a  layer  of  mesothelial  cells.  The  presence  of  stomata 
in  the  pleural  mesothelium  is  denied  by  Miller.  The  blood-vessels 
of  the  visceral  layer  of  the  pleura  arise,  according  to  Miller,  from 
the  pulmonary  artery,  these  forming  a  wide-meshed  network,  which 
empty  into  veins  which  pass  into  the  substance  of  the  lung.  Sen- 
sory nerve-endings,  similar  to  those  found  in  connective  tissue,  have 
been  observed  in  the  parietal  layer  of  the  pleura. 


K  THE  THYROID  GLAND, 

The  thyroid  gland  is  developed  from  three  sources:  Its  middle 
portion,  the  isthmus  of  the  gland,  and  a  portion  of  the  lateral  lobes 
originate  as  a  diverticulum  of  the  pharyngeal  epithelium,  from  what 


\bff 

Fig.  257. — Portion  of  a  cross-section  of  thyroid  gland  of  a  man;   X  3°-      "^'^j  Interstitial 
connective  tissue ;  bg,  blood-vessel  ;   c,  colloid  substance  ;  ts,  gland  alveoli. 


is  later  the  foramen  caecum  of  the  tongue;  a  part  of  both  lateral 
portions,  the  right  and  left  lobes,  are  formed  from  a  complicated 
metamorphosis  of  the  epithelium  of  the  fourth  visceral  pouch.  These 
various  parts  unite  in  man  into  one,  so  that  in  the  adult  the  struc- 
ture of  the  organ  is. continuous.  The  thyroid  gland  consists  of 
numerous  noncommunicatine  acini  or  follicles  of  various  sizes  lined 


320 


ORGANS    OF    RESPIRATION. 


by  a  nearly  cubic  epithelium ;  the  lobules  are  separated  from  each 
other  by  a  highly  vascularized  connective  tissue,  continuous  with 
the  firm  connective-tissue  sheath  surrounding  the  whole  gland. 
The  connective-tissue  frame worlc  of  the  thyroid  has  been  studied  by 
Flint  by  means  of  the  destructive  digestion  method.  Relatively  greater 
amounts  of  connective  tissue  are  found  in  connection  with  the  blood- 
vessels, while  the  follicular  membranes  are  delicate.  The  follicles 
are  either  round,  polyhedral,  or  tubular,  and  are  occasionally 
branched  (Streiff).  At  an  early  stage  the  acini  are  found  to  con- 
tain a  substance  known  as  "colloid"  material. 

Langendorff  has  shown  that  two  varieties  of  cells  exist  in 
the  acini  of  the  thyroid  body — the  chief  cells  and  colloid 
cells.  Those  of  the  first  variety  apparently  change  into  colloid 
cells,  while  the  latter  secrete  the  colloid  substance.  During  the 
formation  of  this  material  the  colloid  cells  become  lower,  and  their 
entire  contents,  including  the  nuclei,  change  into  the  colloid  mass. 
Hürthle  distinguished  two  processes  of  colloid  secretion  ;  in  the  one 
the  cells  remain  intact,  in  the  other  they  are  destroyed.  He  claims 
that  the  colloid  cells  of  Langendorff  participate  in  the  former  pro- 
cess, while  in  the  latter  they  are  first  modified  (flattened)  and  then 
changed  into  the  colloid  substance.  The  secretion  is  formed  in  the 
cells  in  the  form  of  secretory  granules.  The  colloid  material  may 
enter  the  lymph-channels,  either  directly  by  a  rupture  of  the  acini, 
or  indirectly  by  a  percolation  of  the  substance  into  the  intercellular 
clefts,  whence  it  is  carried  into  the  larger  lymphatics. 

The  thyroid  gland  has  a  very  rich  blood  supply.  The  vessels, 
which  enter  through  the  capsule,  break  up  into  smaller  branches 
which  form  a  very  rich  capillary  network  surrounding  the  follicles. 
The  veins,  which  are  thin-walled,  arise  from  this  capillary  network. 
The  gland  is  provided  with  a  rich  network  of-  lymphatic  vessels. 

Anderson  (91)  and  Berkley  (94)  have  studied  the  distribution 
of  the  nerve-fibers  of  the  thyroid  gland  with  the  chrome-silver 
method  ;  the  account  given  by  the  latter  is  the  more  complete  and 
will  be  followed  here.  The  nonmedullated  nerves  entering  the  gland 
form  plexuses  about  the  larger  arteries,  which  are  less  dense  around 
the  smaller  arterial  branches.  Some  of  these  nerve-fibers  are  vascular 
nerves  and  end  on  the  vessels  ;  others  form  perifollicular  meshes 
surrounding  the  follicles  of  the  gland.  From  the  network  of  nerve- 
fibers  about  the  follicles,  Berkley  was  able  to  trace  fine  nerve  fila- 
ments which  seemed  to  terminate  in  end-knobs  on  or  between  the 
epithelial  cells  lining  the  follicles.  Even  in  the  best  stained  prepa- 
rations, however,  not  nearly  all  the  follicular  cells  possess  such  a 
nerve  termination.  In  methylene-blue  preparations  of  the  thyroid 
gland  (Dr.  De  Witt)  some  few  medullated  fibers  were  found  in  the 
nerve  plexus  surrounding  the  vessels.  In  a  number  of  preparations 
these  were  traced  to  telodendria  situated  in  the  adventitia  of  the 
vessels,  showing  that  at  least  a  portion  of  these  medullated  nerves 
are  sensory  nerves  ending  in  the  walls  of  the  vessels. 


THE    THYROID    GLAND. 


321 


PARATHYROID  GLANDS. 

Small  glandular  structures  found  on  the  posterior  surfaces  of  the 
lateral  lobes  of  the  thyroid  were  discovered  by  Sandström  in  1880. 
They  are  surrounded  by  a  thin  connective-tissue  capsule  and  divided 
into  small  imperfectly  developed  lobules  by  a  few  thin  fibrous-tissue 
septa  or  trabeculae,  which  support  the  larger  vessels.  The  epithelial 
portions  of  these  structures  consist  of  relatively  large  cells  and  capil- 
lary spaces.  According  to  Schaper  (95),  who  has  recently  subjected 
these  structures  to  a  careful  investigation,  the  epithelial  cells  have 
a  diameter  which  varies  from  10  //to  12  //,  possessing  nuclei  4  // 
in  diameter.  These  cells  are  of  polygonal  shape  and  have  a  thin 
cell-membrane,  a  slightly  granular  protoplasm,  and  a  nucleus  pre- 
senting a  delicate  chromatic  network.  The  cells  are  arranged  either 
in  larger  or  smaller  clusters  or,  in  some  instances,  in  anastomosing 
trabecule  or  columns,  consisting  either  of  a  single  row  or  of  several 
rows  of  cells.   Between  the  clusters  or  columns  of  cells  are  found  rela- 


Fig.  258. — From  parathyroid  of  man. 

lively  large  capillaries,  the  endothelial  lining  of  which  rests  directly 
on  the  epithelial  cells.  Connective-tissue  fibrils  do  not,  as  a  rule, 
follow  the  capillaries  between  the  cell-masses.  These  vessels  may 
therefore  be  regarded  as  sinusoids  (Minot).  The  structure  of  the 
parathyroid  resembles  in  many  respects  that  of  certain  embryonic 
stages  of  the  thyroid,  and  it  has  been  suggested  that  these  bodies 
represent  small  masses  of  thyroid  gland  tissue,  retaining  their  em- 
bryonic structure.  Schaper  has  observed  parathyroid  tissue,  the 
cells  of  which  were  here  and  there  arranged  in  the  form  of  small 
follicles,  some  of  which  contained  colloid  substance.  Such  obser- 
vations lend  credence  to  the  view  regarding  the  parathyroid  as  an 
embryonic  structure.  Whether  in  this  stage  they  form  a  special 
secretion  has  not  been  fully  determined.     (See  Schaper,  95.) 


322  ORGANS    OF    RESPIRATION. 


TECHNIC. 

For  the  demonstration  of  the  larynx  and  trachea,  young  and 
healthy  subjects  should  be  selected.  Pieces  of  the  mucous  membrane  or 
the  whole  organ  should  be  immersed  in  a  fresh  condition.  Sections 
through  the  entire  organ  present  only  a  general  structural  view ;  but  if 
a  close  examination  of  accurately  fixed  mucous  membrane  be  desired,  the 
latter  should  be  removed  with  a  razor  before  sectioning  and  treated 
separately. 

Chromic-osmic  acid  mixtures  are  recommended  as  fixing  agents, 
and  safranin  as  a  stain.  Besides  the  nuclear  differentiation,  the  goblet  cells 
stain  brown,  and  the  elastic  network  of  the  stratum  proprium  and  the 
submucosa  a  reddish -brown. 

For  examining  the  epithelium,  isolation  methods  are  employed,  such 
as  the  Yi  alcohol  of  Ranvier. 

The  examination  of  the  respiratory  epithelium  is  attended  with 
peculiar  difficulty ;  it  is,  perhaps,  best  accomplished  by  injecting  a 
0.5^  solution  of  silver  nitrate  into  the  bronchus  until  the  lumen  is 
completely  filled,  and  then  placing  the  whole  in  a  0.5^  solution  of  the 
same  salt.  After  a  few  hours,  wash  with  distilled  water  and  transfer  to 
70^  alcohol.  Thick  sections  are  now  cut  and  portions  of  the  respiratory 
passages  examined  ;  the  silver  lines  represent  the  margins  of  the  epithe- 
lial cells.  Such  sections  should  not  be  fastened  to  the  slide  with  albumen, 
as  the  latter  soon  darkens  and  blurs  the  picture.  These  specimens  may 
also  be  stained. 

For  the  elastic  fibers,  especially  those  of  the  alveoli,  fixation  in 
Müller' s  fluid  or  in  alcohol  and  staining  with  orcein  is  a  good 
method,  as  also  Weigert's  differential  elastic  tissue  stain.  Fresh  pieces 
of  lung  tissue  treated  with  potassium  hydrate  show  numerous  isolated  elastic 
fibers. 

Pulmonary  tissue  may  be  treated  by  Golgi's  method,  which 
brings  out  a  reticular  connective-tissue  structure  in  the  vessels  and  alveoli. 

The  pulmonary  vessels  may  be  injected  with  comparative  ease. 

The  thyroid  gland  is  best  fixed  in  Flemming's  solution  ;  it  is 
then  stained  with  M.  Heidenhain's  hematoxylin  solution  or,  better  still, 
with  the  Ehrlich-Biondi  mixture  which  differentiates  the  chief  from  the 
colloid  cells  ;  the  former  do  not  stain  at  all,  while  the  latter  appear  red 
with  a  green  nucleus  (Langendorff).  The  colloid  substance  of  the  thy- 
roid gland  does  not  cloud  in  alcohol  or  chromic  acid,  nor  does  it  coagu- 
late in  acetic  acid,  but  swells  in  the  latter;  33%  potassium  hydrate 
hardly  causes  the  colloid  material  to  swell  at  all,  though  in  weaker  solu- 
tions it  dissolves  after  a  long  time. 


THE    URINARY    ORGANS.  323 


V.  THE   GENITO-URINARY   ORGANS. 

A.  THE  URINARY  ORGANS. 

J.  THE  KIDNEY. 

The  kidney  is  a  branched  tubular  lobular  gland,  which  in  man 
consists  of  from  ten  to  fifteen  nearly  equal  divisions  of  pyramidal 
shape  known  as  the  renal  lobes.  The  apex  of  each  pyramid  (the 
Malpighian  pyramid)  projects  into  the  pelvis  of  the  kidney.  The 
kidney  is  surrounded 
by  a  thin  but  firm  cap- 
sule consisting  of  fib- 
rous connective  tissue  ^  — ^*@s.i ..„...^«^  .M^^^-^m>f   „«!»—    rtery. 


containing  a  few  elas- 
tic fibers    and,    in  its      Vein.  _j 
deeper  portion,  a  thin 
layer    of    nonstriated  .,         ^         ,        .  ,        ,      . 

■'       ,  ,,  Fig.   259. — Kidney  of  new-born  infant,  showing  a 

muscle-cells.  distinct  separation  into   reniculi ;  natural   size.     At  a  is 

The  secreting  por-       seen  the  consolidation  of  two  adjacent  reniculi. 

tion  is  composed  of  a 

large  number  of  tubules  twisted  and  bent  in  a  definite  and  typical 
manner,  the  uriniferoiis  tubules.  In  each  one  of  these  tubules  we 
distinguish  the  following  segments  :  (i)  Bozvman' s  capsule,  or  the 
ampulla,  surrounding  a  spheric  plexus  of  capillaries,  the  glomerulus, 
which,  with  the  capsule  of  Bowman,  forms  a  Malpighiaii  corpuscle  ; 
(2)  a  proximal  convoluted  portion ;  (3)  a  U-shaped  portion,  con- 
sisting of  straight  descending  and  ascending  limbs  and  the  loop 
of  Henle ;  (4)  a  distal  convoluted  portion  or  intercalated  portion ; 
and  (5)  an  arched  collecting  portion  ;  from  the  confluence  of  a  num- 
ber of  these  are  formed  the  larger  straight  collecting  tubules,  which, 
in  turn,  finally  unite  to  form  the  papillary  ducts  or  tubules  of 
Bellini,  which  pass  through  the  renal  papillae  and  empty  into  the 
renal  pelvis.  Besides  the  uriniferous  tubules  the  kidney  con- 
tains a  complicated  vascular  system,  a  small  amount  of  connective 
tissue,  etc. 

In  a  longitudinal  median  section  the  kidney  is  seen  to  be  com- 
posed of  two  substances, — the  one,  the  medullary  substance,  pos- 
sessing relatively  few  blood  capillaries  and  containing  straight 
collecting  tubules  and  the  loops  of  Henle  ;  the  other,  the  cortical 
substance,  richer  in  blood-vessels,  and  containing  principally  the 
Malpighian  corpuscles  and  the  proximal  and  distal  convoluted  tu- 
bules. In  each  renal  lobe  we  find  these  two  substances  distributed 
as  follows  :  The  Malpighian  pyramid  consists  entirely  of  medullary 
substance,  which  sends  out  a  large  number  of  processes,  the  medul- 


324 


THE    GENITO-URINARY    ORGANS. 


lary  rays,  or  pyramids  of  Ferrein,  toward  the  surface  of  the  kidney. 
The  latter  do  not,  however,  quite  reach  the  surface,  but  terminate  at 
a  certain  distance  below  it ;  they  are  formed  by  collecting  tubules 
which  extend  beyond  the  medullary  substance.  The  entire  remain- 
ing portion  of  the  kidney  is  composed  of  cortical  substance ;  be- 
tween the  medullary  rays  it  forms  the  cortical  processes,  and  at  the 
periphery  of  the  kidney,  where  the  medullary  rays  are  absent,  the 
cortical  labyrijtth.  Those  portions  of  the  cortical  substance  sep- 
arating the  Malpighian  pyramids  are  known  as  the  columns  of 
Berti7ii,  or  septa  renis. 


—    d 


Fig.  260. — Isolated  uriniferous  tubules  :  A  and  B,  from  mouse ;  C,  from  turtle. 
In  all  three  figures  a  represents  the  Malpighian  corpuscle ;  b,  the  proximal  convoluted 
tubule;  c,  the  descending  limb  of  Henle's  loop;  d,  Henle's  loop;  e,  the  straight  col- 
lecting tubule  ;  f,  the  arched  collecting  tubule. 


The  various  segments  of  the  uriniferous  tubule  are  characterized 
by  their  shape  and  size  and  by  their  epithelial  lining. 

The  Malpighian  corpuscle  has  a  diameter  of  from  120^  to  220  fi. 
The  capsule  surrounding  the  glomerulus  consists  of  two  layers, 
which  are  to  be  distinguished  from  each  other  when  its  relation  to 
the  glomerulus  is  taken  into  consideration.  The  capsule  forms  a 
double-walled  membrane  around  the  glomerulus ;  a  condition 
which  is  easily  understood  by  imagining  an  invagination  of  the 


THE    URINARY    ORGANS. 


125 


glomerulus  into  the  hollow  capsule.  Between  the  inner  wall  cov- 
ering the  surface  of  the  glomerulus  (glomerular  epithelium)  and  the 
outer  wall  (Bowman's  capsule)  there  remains  a  cleft-like  space 
which  communicates  with  the  lumen  of  the  corresponding  urinifer- 
ous  tubule.  In  the  adult  the  glomerular  epithelium  is  very  flat, 
with  nuclei  projecting  slightly  into  the  open  space  of  the  Malpig- 
hian  corpuscle.  The  epithelium  of  the  outer  wall  is  somewhat 
higher,  but  still  of  the  squamous  type.  The  capsule  of  Bowman 
communicates  with  the  proximal  convoluted  tubule  by  means  of  a 
short  and  narrow  neck.     Its  epithelium  passes  over  gradually  into 


Column  of  Ber-  ^ 
tini.  "~~ 

Medullary  '^'' 
rays. 

Malpighian 
pyramid. 

Lobule  of  adi- 
pose tissue. 


Blood-vessel. \. 


Papilla. 


-^--Ureter. 


Fig.  261. — Median  longitudinal  section  of  adult  human  kidney ;  nine-tenths  natural 
size.  In  the  peripheral  portion  the  limits  between  its  renal  lobes  are  no  longer  recogniz- 
able. 


the  cubical  epithehum  of  the  neck,  which,  in  turn,  merges  into  that 
of  the  proximal  convoluted  tubule. 

The  proximal  convoluted  portion  is  from  40  [jl  to  yo  fx  in  diameter 
and  is  lined  by  a  single  layer  of  irregular  columnar  cells,  the 
boundaries  of  which  are  made  out  with  difficulty.  The  structure 
of  these  cells  has  been  studied  in  recent  years  by  a  number  of  in- 
vestigators, among  whom  may  be  mentioned  Disse,  whose  account 


326 


THE    GENITO-URINARY    ORGANS. 


is  here  followed.  In  the  epithelial  cells  of  the  proximal  convoluted 
portion  there  may  be  recognized  an  outer  or  basal  portion  of  the 
cells,  in  which  there  is  found  a  spongioplastic  network  with  rectan- 
gular meshes,  with  cytoreticular  fibrils  running  parallel  and  at 
right  angles  to  the  basement  membrane.  In  the  meshes  of  this 
network  there  is  found  hyaloplasm.  The  cytoreticular  fibrils  which 
are  at  right  angles  to  the  basement  membrane  contain  numerous 
granules,  giving  the  basal  portions  of  the  cells  a  striated  appear- 
ance. The  inner  portions  of  the  cells  contain  a  cytoreticulum  and 
hyaloplasm;  the  reticular  fibrils  do  not,  however,  contain  granules. 


Fig.  262. — From  section  of  cortical  substance  of  human  kidney ;  X  240 :  a,  Epi- 
thelium of  Bowman's  capsule;  b  and  d,  membrana  propria;  c,  glomerular  epithelium; 
e,  blood-vessels  ;  /,  lobe  of  the  glomerulus  ;  g,  commencement  of  uriniferous  tubule ; 
h,  epithelium  of  the  neck ;  i,  epithelium  of  proximal  convoluted  tubule. 


the  inner  portions  of  the  cells  presenting,  therefore,  a  much  less 
striated  appearance  than  the  outer  portions.  In  tissues  not  well 
fixed  there  is  often  observed  in  the  cells  a  free  border  which  presents 
the  appearance  of  being  made  of  stiff  fibrils  or  coarse  and  short 
cilia,  which  has  been  interpreted  as  a  distinctive  structure.  Such  a 
striated  border  is  in  all  probability  a  result  of  partial  disintegration 
or  maceration  of  the  cells.  The  nucleus  of  these  cells  is  of  nearly 
spheric  shape  and  is  situated  in  the  inner  part  of  the  basal  portions 
of  the  cells.  The  cells,  especially  in  their  inner  non-striated  regions, 
are  so  intimately  connected  that  the  cell  limits  are  not  always  dis- 
tinguishable.     In  the  guinea-pig  the  basal  regions   of   the   lateral 


THE  URINARY  ORGANS. 


327 


surfaces  of  the  cells  constituting  the  epithelium  of  the  proximal 
convoluted  portion  present  numerous  projections  which  interlock 
and  give  to  a  surface  view  an  irregular  fringe-like  outline.  In  cross- 
section  the  cells  appear  to  be  striated  from  their  bases  upward  to 
the  middle  of  the  nucleus.  Here,  however,  the  striation  is  without 
doubt  due  to  the  outlines  of  the  irregular  ridges.  (Fig.  264.) 
These  structural  relations  have  lately  been  confirmed  in  the  case 
of  the  guinea-pig,  and  also  found  to  hold  true  for  man  (Landauer). 
This  striation  is  much  coarser  than  that  found  in  the  basal  portions 
of  the  cells,  but  both  are,  under  certain  circumstances,  seen  together. 


Nuclei  of  en- 
d  o t h  e  1  ial 
cells  of  blood 
capillaries. 

Lumen  of 
uriniferous 
tubule. 

Striated 
border. 


Fig.  263. — Section  of  proximal  convoluted  tubules  from  man  ;      X  S^O. 


The  proximal  convoluted  portion  of  the  uriniferous  tubule,  before 
it  terminates,  passes  over  into  a  straighter  portion,  which  gradu- 
ally becomes  smaller  in  diameter,  and  is  situated  in  the  medullary 
rays.  This  portion  of  the  uriniferous  tubule,  which  is  sometimes 
designated  as  the  sph'al  segment  of  Schachowa,  or  again  as  the  end 
segment  of  Argutinski,  is  lined  by  an  epithehum  which  is  similar 
to  that  of  the  proximal  convoluted  portion,  as  above  described. 
The  attenuated  end  of  the  spiral  segment  is  continuous  with  the 
descending  limb  of  Henle's  loop. 

The  descending  limb  of  Henle's  loop,  from  9/i  to  i  5  //  in  diameter, 
is   narrow  and  possesses   flattened  epithelial   cells,  the   centers  of 


328 


THE    GENITO-URINARY    ORGANS. 


which,  containing  the  nuclei,  project  into  the  lumen  of  the  tubule. 
These  central  projections  of  the  cells  are  not  directly  opposite  those 
of  the  cells  on  the  opposite  wall,  but  alternate  with  the  latter,  thus 


Nucleus. 


r';sfST~  Nucleus. 


Fig.  264. — Epithelium  from  proximal  convoluted  tubule  of  guinea-pig,  with  surface 
and  lateral  views  (chrome- silver  method)  ;  X  59°  '  ^>  ^»  The  irregular  interlacing  pro- 
jections. 


Ä 


">    » 


l;^/r 


/ 


^*^.      V\ 


'^  't^^^^>' 


^€.*> 


Fig.  265. — From  cortical  portion  of  longitudinal  section  of  kidney  of  young  child. 


giving  to  the  lumen  a  zigzag  outline  corresponding  to  the  length 
of  the  cell.  The  thick  portion  of  the  loop,  for  the  most  part  repre- 
sented by  the  ascending  limb,  but  generally  embracing  the  loop  itself, 


THE    URINARY    ORGANS. 


329 


from  23  /i  to  28  fj.  in  diameter,  possesses  a  columnar  epithelium 
similar  to  that  of  the  proximal  convoluted  portion.  Here,  however, 
the  basal  striation  of  the  cells  is  not  so  distinct,  the  lumen  is  some- 
what larger  than  that  of  the  descending-  limb,  and  by  treatment 
with  certain  reagents  the  epithelium  may  often  be  separated  as  a 
whole  from  the  underlying;  basement  membrane. 

The  distal  convoluted  or  intercalated  portion  (segment  of 
Schweigger- Seidel),  from  39  (x  to  45  fi  in  diameter,  is  only  slightly 
curved  (2  to  4  convolutions).  Its  epithelium  is  relatively  high, 
though  not  so  high  as  that  lining  the  proximal  convoluted  portion 
and  not  so  distinctly  striated,  though  containing  numerous  granules. 
The  cells  are  provided  with  large  nuclei  and  their  basal  portions  are 
joined  by  interlacing  projections. 


Fig.    266.— Section  of  medulla  of  human  kidney ;    X  about  300 :  a,  a,  a.  Ascending 


The  next  important  segment  is  the  short  arched  collecting  portion, 
which  has  nearly  cubical  epithelial  cells  and  a  lumen  somewhat  wider 
than  that  of  the  intercalated  tubule.  The  smaller  straight  collecting 
tubules  have  a  low  columnar  epithelium  with  cells  of  somewhat  ir- 
regular shape,  the  basal  portions  of  which  are  provided  with  short, 
irregular,  intertwining  processes,  which  serve  to  hold  the  cells  in 
place.  The  diameter  of  the  collecting  tubules  measures  from  45  // 
to75/i. 


330 


THE    GENITO-URINARY    ORGANS. 


In  the  larger  collecting  tubules  the  epithelium  is  more  regular 
and  becomes  higher  as  the  tube  widens.  These  tubules  gradually 
unite  within  the  Malpighian  pyramid  and  the  regions  adjacent  to 
the  columns  of  Bertini  to  form  1 5  to  20  papillary  ducts  from  200  fj. 
to  300  //  in  diameter.  The  latter  have  a  high  columnar  epithelium, 
and  empty  into  the  pelvis  of  the  kidney  at  the  apex  of  the  papilla, 
forming  the  formnina  papillaria  in  an  area  known  as  the  area 
cribrosa. 

Besides  the  epithelium,  the  uriniferous  tubules  possess  an  ap- 
parently structureless  membrana  propria,  that  of  the  collecting 
tubules  being  very  thin.  This  membrane  may  be  isolated,  as  has 
been  shown  by  F.  P.  Mall,  by  macerating  frozen  sections  in  a  cold 
saturated  solution  of  bichromate  of  soda  for  several  days.  This 
membrane  is  digested  in  pancreatin. 


Papillary  duct. 
I 


Blood-vessel. 


Fig.  267. — From  longitudinal  section  through  papilla  of  injected  kidney  ;  X  4°  =  ^>  -^pi" 
thelium  of  collecting  tubule  under  greater  magnification. 


Between  the  Malpighian  pyramids  are  found  the  columns  of 
Bertini,  presenting  a  structure  similar  to  that  of  the  cortex  of  the 
kidney,  and  extending  to  the  hilum  of  the  kidney. 

Between  the  uriniferous  tubules  and  surrounding  the  blood- 
vessels of  the  kidney  there  is  found  normally  a  small  amount  of 
stroma  tissue,  consisting  of  white  fibrous  and  reticular  fibers,  elastic 
fibers  being  found  in  connection  with  the  blood-vessels  (F.  P.  Mall, 
Riihle).  Between  the  convoluted  portions  of  the  tubules  this  is 
present  only  in  small  quantity,  the  fibrils  being  felted  to  form 
sheaths  for  the  tubules  ;  a  somewhat  greater  amount  being  found 
in  the  neighborhood  of  the  Malpighian  corpuscles,  in  the  boundary 
zone  between  the  cortex  and  medulla  and  between  the  larger  col- 
lecting tubules  in  the  apices  of  the  Malpighian  pyramids. 

From  what  has  been  said  concerning  the  uriniferous  tubule  it 
must  be  evident  that  its  course  is  a  very  tortuous  one.      Beginning 


THE    URINARY    ORGANS.  331 

with  the  Malpighian  corpuscles,  situated  in  the  cortex  between  the 
medullary  rays,  the  tubule  winds  from  the  cortex  to  the  medulla 
and  back  again  into  the  cortex,  where  it  ends  in  a  collecting  tubule, 
which  passes  to  the  medulla  to  terminate  at  the  apex  of  a  Malpig- 
hian pyramid.  The  different  portions  of  the  tubules  have  the 
following  positions  in  the  kidney  :  In  the  cortex  between  the  medul- 
lary rays  are  found  the  Malpighian  corpuscles,  the  neck,  the  proxi- 
mal and  distal  convoluted  portions  of  the  uriniferous  tubule,  and  the 
arched  collecting  tubules.  The  medullary  rays  are  formed  by  the 
cortical  portions  of  the  straight  collecting  tubules  and  a  portion  of 


C,       X3 


Ci^ 


'Boundary  line 
between  two 
Malpig-hian 
pyramids. 


Uriniferous 
tubules. 


■&    <, 


''\ 


Glomerulus. 


)    O 


Fig.  268.— Section  through  junction  of  two  lobules  of  kidney,  showing  their 
coalescence  ;  from  new-born  infant. 

the  descending  and  ascending  limbs  of  Henle's  loops.  The  me- 
dulla is  made  up  mainly  of  straight  collecting  tubules  of  various 
sizes  and  of  the  descending  and  ascending  limbs  and  loops  of 
Henle's  loops,  the  latter  being  often  found  in  the  boundary  zone 
between  the  cortex  and  medulla.  '  (See  Fig.  266.)  The  ascending 
limb  of  Henle's  loop  of  each  uriniferous  tubule,  after  it  enters  the 
cortex,  comes  into  close  proximity  with  the  Malpighian  corpuscle 
of  the  respective  uriniferous  tubule. 


332  THE    GENITO-URINARY    ORGANS. 

The  blood-vessels  of  the  kidney  have  a  characteristic  distribu- 
tion, and  are  in  the  closest  relationship  to  the  uriniferous  tubules. 

The  renal  artery,  as  has  been  shown  by  Brodel,  divides  at  the 
hilum  on  an  average  into  four  or  five  branches,  about  three-fourths 
of  the  blood-supply  passing  in  front  of  the  pelvis,  while  one-fourth 
runs  posteriorly.  The  portion  of  the  kidney  supplied  by  the  anterior 
branches  is  in  its  blood-supply  quite  distinct  from  that  supplied  by  the 
posterior  branches ;  the  one  set  of  branches  do  not  cross  over  to  the 
other.  The  two  ends  of  the  kidney  are  supplied  by  an  anterior 
and  a  posterior  branch,  each  of  which  generally  divides  into  three 
branches,  which  pass  respectively,  one  anteriorly,  one  posteriorly, 
and  one  around  the  end  of  the  uppermost  and  the  lowest  calyx. 

The  main  branches  of  the  renal  artery  give  off  lateral  branches 
to  the  renal  pelvis,  supplying  its  mucous  membrane  and  then 
breaking  up  into  capillaries  which  extend  as  far  as  the  "area  crib- 
rosa."  The  venous  capillaries  of  this  region  empty  into  veins 
which  accompany  the  arteries.  Besides  these,  other  arteries  origi- 
nate from  the  principal  branches,  or  from  their  immediate  offshoots, 
and  pass  backward  to  supply  the  walls  of  the  renal  pelvis,  the 
renal  capsule,  and  the  ureter.  The  main  trunks  themselves  pene- 
trate at  the  hilum,  and  divide  in  the  columns  of  Bertini  to»  form 
arterial  arches  (arteriae  arciformes)  which  extend  between  the  cortical 
and  medullary  substances.  Numerous  vessels,  the  intralobular 
arteries,  originate  from  the  arterise  arciformes  and  penetrate  into  the 
cortical  pyramids  between  the  medullary  rays.  Here  they  give  off 
numerous  twigs,  each  of  which  ends  in  the  glomerulus  of  a  Mal- 
pighian  corpuscle.  These  short  lateral  twigs  are  the  vasa  afferentia. 
Each  glomerulus  is  formed  by  the  breaking  down  of  its  afferent 
vessel,  which,  on  entering  the  Malpighian  corpuscle,  divides  into  a 
number  of  branches,  five  in  a  glomerulus  of  a  child  three  months 
old  reconstructed  by  W.  B.  Johnston,  each  in  turn  subdividing  into 
a  capillary  net.  From  each  of  these  nets  the  blood  passes  into 
a  somewhat  larger  vessel  constituting  one  of  the  branches  of  the 
efferent  vessel  which  carries  the  blood  away  from  the  glomerulus. 
Since  the  afferent  and  efferent  vessels  lie  in  close  proximity,  the 
capillary  nets  connecting  them  are  necessarily  bent  in  the  form  of 
loops.  The  groups  of  capillaries  in  a  glomerulus  are  separated  from 
each  other  by  a  larger  amount  of  connective  tissue  than  separates 
the  capillaries  themselves,  so  that  the  glomerulus  may  be  divided 
into  lobules.  In  shape  the  glomerulus  is  spheric,  and  is  covered 
by  a  thin  layer  of  connective  tissue  over  which  lies  the  inner  mem- 
brane of  the  capsule,  the  glomerular  epithelium.  On  its  exit  from 
the  glomerulus  the  vas  efferens  separates  into  a  new  system  of 
capillaries,  which  gradually  becomes  venous  in  character.  Thus,  the 
capillaries  which  form  the  glomerulus,  together  with  the  vas  efferens, 
are  arterial,  and  may  be  included  in  the  category  of  the  so-called 
arterial  retia  mirabilia.  Those  capillaries  formed  by  the  vas  efferens 
after  its  exit  from  the  Malpighian  corpuscle  lie  both  in  the  medullary 


THE    URINARY    ORGANS. 


333 


rays  and  in  the  cortical  pyramids.  The  meshes  of  the  capillary  net- 
works distributed  throughout  the  medullary  rays  are  considerably 
longer  than  those  of  the  networks  supplying  the  cortical  pyramids 
and  labyrinth,  the  latter  being  quadrate  in  shape.  The  glomeruli 
nearest  the  renal  papillae  give  off  longer  vasa  efferentia  which  extend 
into  the  papillary  region  of  the  Malpighian  pyramids  (arteriolae 
rectae  spuriae)  and  form  there  capillaries  which  ramify  throughout 
the  papillse  with  oblong  meshes. 


Artery  of 
capsule. 


Arched  collecting 
tubule. 

Straight  collect- 
ing tubule. 

Distal  convoluted 
tubule. 

Malpighian    cor- 
puscle. 

Proximal    convo- 
luted tubule. 
Loop  of  Henle. 

Collecting  tubule. 


Arteria  arcuata. 


Large  collecting 
tubule. 


Papillary  duct. 


Glomerulus. 


Vena  arcuata, 


Fig.  269. 


-Diagrammatic  scheme  of  uriniferous  tubules  and  blood-vessels  of  kidney. 
Drawn  in  part  from  the  descriptions  of  Golubew. 


Arterial  retia  mirabiHa  also  occur  in  the  course  of  the  vasa 
afferentia  between  the  intralobular  arteries  and  the  glomeruli,  but 
nearer  the  latter.  Each  is  formed  by  the  breaking  down  of  the  small 
afferent  vessels  into  from  two  to  four  smaller  branches,  which  then 
reunite  to  pass  on  as  a  single  vessel.  In  structure  these  retia  differ 
greatly  from  the  glomeruli  in  that  here  the  resulting  twigs  are  not 
capillaries  and  have  nothing  to  do  with  the  secretion  of  urine 
(Golubew). 

From   the  vasa  afferentia  arterial  twigs  are  occasionall}'  given 


334  THE    GENITO-URINARY    ORGANS.  ' 

off,  which  break  down  into  capillaries  within  the  cortical  substance. 
Other  arteries  originate  from  the  lower  portion  of  the  intralob- 
ular arteries  or  from  the  arciform  arteries  themselves  and  enter 
the  medullary  substance,  where  they  form  capillaries.  These 
vessels  constitute  the  so-called  "  arteriolae  rectae  verae."  Their 
capillary  system  is  in  direct  communication  with  the  capillaries 
of  the  vasa  afferentia  and  "  vasa  recta  spuria."  The  intralobular 
arteries  are  not  entirely  exhausted  in  supplying  the  vasa  afferentia 
which  pass  to  the  glomeruli.  A  few  extend  to  the  surface  of  the 
kidney  and  penetrate  into  the  renal  capsule,  where  they  termin- 
ate in  capillaries  which  communicate  with  those  of  the  recur- 
rent, suprarenal,  and  phrenic  arteries,  etc.  Smaller  branches 
from  these  latter  vessels  may  penetrate  the  cortex  and  form 
glomeruli  of  their  own  in  the  renal  parenchyma  (arteriae  capsulares 
glomeruliferae).  These  relations,  first  described  by  Golubew,  are 
of  importance  not  only  in  the  establishment  of  a  collateral  circula- 
tion, but  also  as  a  partial  functional  substitute  in  case  of  injury  to 
the  renal  arteries.  The  same  author  also  confirms  the  statements 
of  Hoyer  {yj')  and  Geberg,  that  between  the  arteries  and  veins  of 
the  kidney,  in  the  cortical  substance,  in  the  columns  of  Bertini,  and 
at  the  bases  of  the  Malpighian  pyramids,  etc.,  direct  anastomoses 
exist  by  means  of  precapillary  twigs. 

From  the  capillaries  the  venous  blood  is  gathered  into  small 
veins  which  pass  out  from  the  region  of  the  medullary  rays  and 
cortical  pyramids  and  unite  to  form  the  "intralobular  veins."  These 
have  an  arrangement  similar  to  that  of  the  corresponding  arteries. 
The  venous  blood  of  the  labyrinthian  capillaries  also  flows  into  the 
intralobular  veins,  and  as  a  result  a  peculiar  arrangement  of  these 
vessels  is  seen  at  the  surface  of  the  kidney  where  the  capillaries 
pass  radially  toward  the  terminal  branches  of  the  intralobular  veins 
and  form  the  stellate  figures  known  as  the  vence  stellatce.  This  sys- 
tem is  also  connected  with  those  venous  capillaries  of  the  capsule 
which  do  not  empty  into  the  veins  accompanying  the  arteries  of  the 
capsule.  The  capillary  system  of  the  Malpighian  pyramids  unites 
to  form  veins,  the  "venulae  rect^,"  which  empty  into  the  venous 
arches  (venae  arciformes)  which  lie  parallel  with  and  adjacent  to  the 
corresponding  arteries.  The  larger  veins  are  found  side  by  side 
with  the  arteries  and  pass  out  at  the  hilum  of  the  organ. 

Lymphatics  of  the  kidney  may  be  divided  into  superficial 
lymphatic  vessels,  situated  in  the  capsule,  and  deep  ones,  found  in 
the  substance  of  the  kidney.  The  deep  lymphatic  vessels  need  to 
be  investigated  further.  They  form  a  network  of  closed  lymphatic 
vessels  throughout  the  cortex.  These  empty,  according  to  Rin- 
dowsky,  into  larger  lymphatics,  which  follow  the  intralobular  ves- 
sels ;  and,  according  to  Stahr,  into  larger  vessels  situated  in  the 
medullary  rays.  The  lymphatic  vessels  of  the  kidney  proper 
(deep  vessels)  leave  this  organ  at  the  hilum. 

The  kidneys  receive  their  innervation  through  nonmedullated 


THE    URINARY    ORGANS. 


335 


and  medullated  nerve-fibers.  The  former  accompany  the  arteries 
and  may  be  traced  along  these  to  the  Malpighian  corpuscles. 
From  the  plexuses  surrounding  the  vessels  small  branches  are 
given  off,  which  end  on  the  muscle-cells  of  the  media.  According  to 
Berkley,  small  nerve-fibrils  may  be  traced  to  the  uriniferous  tubules, 
which  pierce  the  membrana  propria  and  end  on  the  epithelial  cells. 
Smirnow  has  also  traced  nerve-fibers  to  the  epithelial  cells  of  the 
uriniferous  tubules  and  the  Malpighian  corpuscles.  Dogiel  has 
shown  that  medullary  (sensory)  nerve-fibers  terminate  in  the 
adventitia  of  the  arteries  of  the  capsule. 

The  secretory  processes  of  the  kidney  can  be  considered  only 
briefly  in  this  connection.  The  theories  concerning  uriniferous 
secretion  may  be  grouped  under  two  heads  :  namely,  the  theory 
of  C.  Ludwig,  who  believed  that  all  the  constituents  of  the  urine 


Fig.  270. — A,  Direct  anastomosis  between  an  artery  and  vein  in  a  column  of  Bertin 
of  child  ;  B,  bipolar  rete  mirabile  inserted  in  the  course  of  an  arterial  twig.  Dog's 
kidney  (after  Golubew). 


leave  the  blood  through  the  glomeruli,  entering  the  uriniferous 
tubules  as  a  urine  containing  a  large  percentage  of  water,  which 
is  concentrated  in  its  passage  through  the  uriniferous  tubule  by 
the  absorption  of  water  ;  while  according  to  the  theory  of  Bowman, 
and  later  Heidenhain,  only  the  water  and  inorganic  salts  leave  the 
blood  through  the  glomerulus,  and  that  in  the  proportion  found  in 
the  urine,  while  the  urea  is  secreted  by  the  epithelial  cells  of  the 
uriniferous  tubules,  and  mainly  in  those  portions  of  the  tubules 
possessing  a  striated  epithelium.  The  majority  of  writers  who 
have  considered  the  question  of  urinary  excretion  have  directly  or 
indirectly  expressed  themselves  as  adherents  to  one  or  the  other 
of  the  above  theories.  A  number  of  recent  observers  have  departed 
somewhat  from  either  of  the  above  theories,  and  of  these  we  may 


336  THE    GENITO-URINARY    ORGANS. 

mention  especially  the  careful  researches  of  Cushny,  who  brings 
forth  strong  proof  to  show  that  with  the  fluid  passing  through  the 
glomerular  epithelium  there  are  carried  certain  salts  and  urea,  the 
salts  and  urea  in  the  proportion  in  which  they  occur  in  the  blood- 
plasma,  and  that  in  passage  through  the  uriniferous  tubules  a  cer- 
tain percentage  of  the  fluids  and  certain  salts  are  again  absorbed, 
the  salts  in  proportion  to  their  diflusibility  or  their  permeability  of 
the  renal  cells. 

The  permanent  kidney  is  developed  as  early  as  the  fifth  week  of 
embryonic  life.  The  renal  anlagen,  from  which  the  epithelium  of 
the  ureter,  renal  pelvis,  and  a  portion  of  the  uriniferous  tubules  is 
formed,  originate  from  the  median  portion  of  the  posterior  wall  of 
the  Wolffian  duct.  These  buds  grow  with  their  blind  ends  ex- 
tending anteriorly,  and  are  soon  surrounded  by  cellular  areas,  the 
blastema  of  the  kidneys.  After  the  renal  bud  has  become  differ- 
entiated into  a  narrow  tube  (the  ureter)  and  a  wider  central  cavity 
(the  renal  pelvis)  hollow  epithelial  buds  are  developed  from  the 
latter.  These  extend  radially  toward  the  surface  of  the  renal 
anlagen,  Avhere  they  undergo  a  T-shaped  division.  These  latter  are 
the  first  traces  of  the  papillaiy  ducts  and  collecting  tubules.  The 
ends  of  these  T-shaped  divisions  are  surrounded  by  a  cellular  tissue, 
derived  from  the  mesoderm,  which  is  known  as  the  renal  blastema 
or  the  nephrogenic  tissue.  In  this  tissue  there  are  differentiated 
spheric  masses  of  cells,  which  in  their  further  growth  differentiate 
into  S-shaped  structures  one  end  of  which  unites  with  the  ends 
of  the  epithelial  buds,  developed  as  above  described.  The  S-shaped 
structures  acquire  a  lumen  and  form  the  anlagen  of  the  uriniferous 
tubules,  from  the  arched  collecting  tubules  to  and  including 
Bowman's  capsule.  The  ducts  of  the  kidneys,  from  the  papillary 
ducts  to  the  collecting  tubules  of  the  medullary  rays,  have  their 
origin  from  the  epitheHal  buds  which  develop  from  the  side  of  the 
Wolffian  ducts,  while  the  uriniferous  tubules  proper  have  their 
origin  in  the  nephrogenic  tissues. 


2.  THE  PELVIS  OF  THE  KIDNEY,  URETER,  AND  BLADDER» 

The  renal  pelvis,  ureter,  and  urinary  bladder  are  lined  by  strati- 
fied transitional  epithelium.  Its  basal  cells  are  nearly  cubical ; 
these  support  from  two  to  five  rows  of  cells  of  varying  shape.  They 
may  be  spindle-shaped,  irregularly  polygonal,  conical,  or  sharply 
angular,  and  provided  with  processes.  Their  variation  in  form  is 
probably  due  to  mutual  pressure.  The  superficial  cells  are  large 
and  cylindric,  a  condition  characteristic  of  the  ureter  and  bladder. 
Their  free  ends  and  lateral  surfaces  are  smooth,  but  their  bases  pre- 
sent indentations  and  projections  due  to  the  irregular  outlines  of  the 
underlying  cells.  The  superficial  cells  often  possess  two  or  more 
nuclei. 


THE    URINARY    ORGANS. 


337 


The  mucosa  often  contains  diffuse  lymphoid  tissue,  which  is  more 
highly  developed  in  the  region  of  the  renal  pelvis.  Here  also 
there  are  found  folds  or  ridges  of  mucosa  which  extend  into  the 
epithelium  and  present  the  appearance  of  papillae  when  seen  in 
cross-section.  A  few  mucous  glands  are  also  met  with  in  the 
pelvis  and  in  the  upper  portion  of  the  ureter  in  certain  mammals; 
in    man,    however,    no    typical    glands   are    found,    although    solid 


Superficial  epi- 
thelial cells 


—   Mucosa. 


Epithelium. 


Mucosa. 


Inner  longitud- 
inal muscular 
layer. 


Middle  circular 
muscular 
layer. 


Outer  muscular 
layer. 


Fig.  271. — Section  of  lower  part  of  human  ureter  ;  X  I40- 


epithelial  buds,  which  extend  into  the  mucosa  for  a  distance,  have 
been  described.  The  ureter  possesses  two  layers  of  nonstriated 
muscle-fibers — the  inner  longitudinal,  the  outer  circular.  From  the 
middle  of  the  ureter  downward  a  third  external  muscular  layer  is 
found  with  nearly  longitudinal  fibers. 

The  urinary  bladder  has  no  glands,  and  its  musculature  appar- 
ently consists  of  a  feltwork  of  nonstriated  muscle  bundles,  a  condi- 


338 


THE    GENITO-URINARY    ORGANS. 


tion  particularly  well  seen  in  sections  of  the  dilated  organ.  But  even 
here  three  indistinct  muscle  layers  may  be  distinguished,  the  outer 
and  inner  layers  being  longitudinal  and  the  middle  circular.  A 
remarkable  peculiarity  of  these  structures  is  the  extreme  elasticity 
of  their  epithelium,  the  cells  flattening  or  retaining  their  natural 
shape  according  to  the  amount  of  fluid  in  the  cavities  which  they 


t^J'aSB!«!,.        t'" 


/// 


\ 


\'^ 


h. 


^\X^ 


\ 


ep 


(urn. 


thZr 


tP 


Fig.  272. — Transverse  section  of  the  wall  of  the  human  bladder,  giving  a  general 
view  of  its  structure.  X  ^5-  ^P^  Epithelium;  tp,  tunica  propria  or  mucosa ;  S77i,  sub- 
mucosa  ;  ilm,  inner  longitudinal  layer  of  muscle  ;  r»i,  circular  layer  of  muscle  ;  abn,  ex- 
ternal longitudinal  layer  of  muscle  j  ta,  tunica  adventitia. 


line  (compare  London,  Kann).  The  terminal  blood-vessels  of  ..the 
mucosa  of  the  pelvis  of  the  kidney  deserve  special  mention.  The 
capillaries  arise  from  arterioles  which  are  situated  in  the  ridges  of 
the  mucosa  above  mentioned.  The  capillaries  are  peculiar  in  that 
they  are  not  completely  surrounded  by  connective  tissue,  but  are 
in  part  embedded  in  the  epithelium,  the  epithelial  cells  resting  on 
the  endothelial  wall  of  the  capillaries  (Disse).  The  blood-vessels 
of  the  bladder  anastomose  in  the  tunica  adventitia,  smaller  branches 
pass  to  the  muscular  tissue.  The  main  stems  of  the  vessels  form 
a  plexus  in  the  submucosa,  from  which  arise  the  capillaries  of  the 
mucosa.  The  veins  form  submucous,  muscular,  and  subperitoneal 
plexuses  (Fenwick).  Lymphatic  vessels  are  found  only  in  the 
muscular  coat  and  not  in  the  mucosa. 


THE  SUPRARENAL  GLANDS.  339 

The  nerve  supply  of  the  bladder  has  been  studied  by  Retzius, 
Huber,  and  Grünstein  in  the  frog  and  a  number  of  the  smaller 
mammalia.  Numerous  sympathetic  ganglia  are  observed,  situated 
outside  of  the  muscular  coat,  at  the  base  and  sides  of  the  bladder. 
The  neuraxes  of  the  sympathetic  neurones  of  these  ganglia  are 
grouped  into  smaller  or  larger  bundles  which  interlace  and  form 
plexuses  surrounding  the  bundles  of  nonstriated  muscle-cells.  From 
these  plexuses  nerve-fibers  are  given  off,  which  penetrate  the  muscle 
bundles  and  end  on  the  muscle-cells.  The  cell-bodies  of  the  sym- 
pathetic neurones  are  surrounded  by  the  telodendria  of  small 
■  medullated  fibers,  which  terminate  in  the  ganglia.  Passing  through 
the  ganglia  large  medullated  fibers  (sensoiy  nerves)  may  be  ob- 
served which  pass  through  the  muscular  coat,  branch  repeatedly 
in  the  mucosa,  and  lose  their  medullary  sheaths  on  approaching 
the  epithelium  in  which  they  end  in  numerous  telodendria,  the 
small  branches  of  which  terminate  between  the  epithelial  cells. 

The  ureters  are  surrounded  by  a  nerve  plexus  containing  non- 
medullated  and  medullated  nerve-fibers.  The  former  end  on  cells 
of  the  muscular  layers  ;  the  latter  pass  through  the  muscular  layer, 
and  on  reaching  the  mucosa  branch  a  number  of  times  before  losing 
their  medullary  sheaths.  The  nonmedullated  terminal  branches 
form  telodendria,  the  terminal  fibers  of  which  have  been  traced 
between  the  cells  of  the  lining  epithehum  (Huber). 


B.  THE  SUPRARENAL  GLANDS. 

The  suprarenal  gland  is  surrounded  by  a  fibrous-tissue  capsule 
containing  nonstriated  muscle-cells,  blood-  and  lymph-vessels, 
nerves,  and  sympathetic  ganglia.  The  glandular  structure  is  divided 
into  a  cortical  and  a  medullary  portion.  In  the  former  are  distin- 
guished three  layers,  according  to  the  arrangement,  shape,  and 
structure  of  its  cells — an  outer  glomerular  zone,  a  middle  broad  fas- 
cicular zone,  and  an  inner  reticular  zone.  According  to  Flint,  who 
worked  in  F.  P.  Mall's  laboratory,  and  whose  account  will  here  be 
followed,  the  framework  of  the  gland  is  made  up  of  reticulum. 
In  the  glomerular  zone  this  reticulum  is  arranged  in  the  form  of 
septa,  derived  from  the  capsule,  which  divide  this  zone  into  more  or 
less  regular  spaces  of  oval  or  oblong  shape.  In  the  fascicular  zone 
the  reticulum  is  arranged  in  processes  and  fibrils  running  at  right 
angles  to  the  capsule.  In  the  reticular  zone  the  fibrils  form  a  dense 
network,  while  in  the  medulla  the  reticular  fibrils  are  arranged  in 
processes  and  septa  which  outline  numerous  spaces. 

The  gland-cells  of  the  glomerular  zone  are  arranged  in  coiled  col- 
umns of  cells  found  in  the  compartments  formed  by  the  septa  of 
reticulum  above  mentioned.  The  cells  composing  these  columns 
are  irregularly  columnar,  with  granular  protoplasm  and  deeply  stain- 
ing nuclei.     In  the  fascicular  zone  the  cells  are  arranged  in  regular 


340 


THE    GENITO-URINARY    ORGANS. 


columns,  consisting  usually  of  two  rows  of  cells,  and  situated  be- 
tween  the  reticular  processes,  which  run  at  right  angles  to  the  cap- 
sule. The  cells  of  this  zone  are  polyhedral  in  shape,  with  gran- 
ular protoplasm  often  containing  fat  droplets  and  with  nuclei 
containing  little  chromatin.  Similar  cells  are  found  in  the  reticular 
zone,  but  here  they  are  found  in  small  groups  situated  in  the  meshes 
of  the  reticulum.  The  cells  of  the  medullary  substance  are  less 
granular  and  smaller  in  size  than  those  of  the  cortex,  and  are 
grouped  in  irregular,  round,  or  oval  masses  bounded  by  the  septa  of 
reticulum.    These  cells  stain  a  deep  brown  with  chromic  acid  and  its 


Capsule. 


Zona  glomerulosa. 


►    Zona  fasciculata. 


Zona  reticularis. 


Fig.  273. — Section  of  suprarenal  cortex  of  dog  ;  X  ^^o. 


salts  are  therefore  known  as  chromaffin  cells  ;  the  color  cannot  be 
washed  out  with  water — a  peculiarity  which  shows  itself  even  during 
the  development  of  these  elements,  and  which  is  possessed  by  few 
other  types  of  cells.  Numerous  ganglion  cells,  isolated  and  in 
groups,  and  many  nerve-fibers  occur  in  this  portion  of  the  organ. 


THE  SUPRARENAL  GLANDS. 


341 


The  blood-vessels  of  the  suprarenal  glands  are  of  special  interest, 
since  it  has  been  shown  that  the  secretion  of  the  glands  passes 
directly  or  indirectly  into  the  vessels.  The  following  statements 
we  take  from  Flint  :  The  blood-vessels,  derived  from  various 
sources,  form  in  the  dog  a  poorly  developed  plexus,  situated  in  the 
capsule.  From  this  plexus  three  sets  of  vessels  are  derived,  which 
are  distributed  respectively  in  the  capsule,  the  cortex,  and  the 
medulla   of  the   gland.      The  vessels   of   the    capsule   divide   into 


Fig.  274.— Arrangement  of  the  intrinsic  blood-vessels  in  the  cortex  and  medulla  of 
the  dog's  adrenal  (Fig.  17,  Plate  V,  of  Flint's  article  in  "Contributions  to  the  Science 
of  Medicine,"  dedicated  to  Professor  Welch,  1900). 

capillaries,  which  empty  into  a  venous  plexus  situated  in  the 
deeper  portion  of  the  capsule.  The  cortical  arteries  divide  into 
capillaries  which  form  networks,  the  meshes  of  which  correspond 
to  the  arrangement  of  the  cells  in  the  different  parts  of  the  cortex, 
encircling  the  coiled  columns  of  cells  in  the  glomerular  zone, 
while  in  the  fascicular  zone  the  capillaries  are  parallel  with  occa- 
sional anastomoses.  These  capillaries  form  a  fine-meshed  plexus 
in  the  reticular  zone   and  unite  in  the  peripheral  portion    of  the 


342  THE    GENITO-URINARY    ORGANS. 

medulla  to  form  small  anastomosing  veins,  from  which  the  larger 
veins  are  derived.  The  latter  do  not  anastomose,  and  are  therefore 
terminal  veins.  The  arteries  of  the  medulla  pass  through  the 
cortex  without  giving  off  any  branches  until  the  medulla  is  reached, 
where  they  break  up  into  a  capillary  network  surrounding  the  cell 
masses  situated  here.  The  blood  from  this  plexus  may  be  col- 
lected into  veins  of  the  medulla  which  empty  into  the  terminal 
vein  or  some  of  its  larger  branches,  or  may  flow  directly  into 
branches  of  the  venous  tree.  The  endothelial  walls  of  the  capil- 
laries rest  directly  on  the  specific  gland  cells,  with  the  intervention 
here  and  there  of  a  few  reticular  fibrils.  According  to  Pfaundler, 
the  walls  of  the  blood-vessels  of  the  entire  suprarenal  body  consist 
solely  of  the  tunica  intima. 

The  nerves  of  the  suprarenal  glands  have  been  studied  recently 
by  Fusari  and  Dogiel  (94)  ;  the  description  given  by  the  latter  will 
here  be  followed.  Numerous  nerve-fibers,  both  nonmedullated  and 
medullated,  arranged  in  the  form  of  a  plexus  containing  sym- 
pathetic ganglia,  are  found  in  the  capsule.  From  this  plexus 
numerous  small  bundles  and  varicose  fibers  enter  the  cortex,  where 
they  form  plexuses  surrounding  the  columns  of  cells  or  groups  of 
cells  found  in  the  three  zones  of  the  cortex  and  about  the  vessels 
and  capillaries  of  the  cortex.  The  nerve-fibers  of  these  plexuses  are 
on  the  outside  of  the  columns  and  cell  groups  and  do  not  give 
off  branches  which  pass  between  the  cells.  The  nerve  supply  of 
the  medullary  substance  is  very  rich,  and  is  derived  mainly  from 
large  nerve  bundles  which  pass  from  the  plexus  in  the  capsule  to 
the  medulla,  where  they  divide  and  form  dense  plexuses  which 
surround  the  groups  of  gland-cells  and  veins  ;  from  these  plexuses 
fine  varicose  fibers  pass  between  the  gland-cells,  forming  intercel- 
lular plexuses.  In  the  medulla  there  are  found  in  many  animals 
large  numbers  of  sympathetic  cells,  some  isolated,  others  grouped 
to  form  small  ganglia.  Pericellular  networks  surround  the  cell- 
bodies  of  certain  of  these  sympathetic  cells.  (For  further  informa- 
tion concerning  the  suprarenal  glands  consult  Gottschau,  Weldon, 
Hans  Rabl,  C.  K.  Hoffmann  (92),  Pfaundler,  Fhnt,  and  Dogiel.) 

TECHNIC. 

Kidney. — The  arrangement  of  the  cortical  and  medullary  portions 
of  the  kidney  is  best  seen  in  sections  of  the  kidney  of  small  mammalia, 
cut  in  the  proper  direction,  and,  if  possible,  embracing  the  whole  organ. 
If,  on  the  other  hand,  the  finer  epithelial  structures  are  to  be  examined, 
small  pieces  are  first  fixed  in  osmic  acid  mixtures  or  in  corrosive 
sublimate. 

Impregnation  with  silver  nitrate  (method  of  Golgi  or  Cox) 
reveals  some  points  as  to  the  relation  of  the  cells  of  the  uriniferous  tubules 
to  each  other. 

In  order  to  isolate  the  tubules,  thin  strips  of  kidney  tissue  are 
treated  for  from   fifteen   to   twenty  hours  with  pure  hydrochloric  acid 


TECHNIC.  343 

having  a  specific  gravity  of  1.12  (for  this  purpose  kidney  tissue  is  used 
taken  from  an  animal  killed  twenty-four  hours  previously).  It  is  then 
washed,  teased,  and  examined  in  glycerin  (Schweiger-Seidel).  Fuming 
nitric  acid  (4^^),  applied  for  a  few  hours  to  small  pieces  of  tissue,  occa- 
sionally isolates  the  uriniferous  tubules  very  extensively.  The  further 
treatment  is  then  the  same  as  after  hydrochloric  acid.  A  7,$%  potassium 
hydrate  solution  may  also  be  employed.  The  isolated  pieces  are,  however, 
not  easily  preserved  permanently. 

The  epithelium  of  the  uriniferous  tubules  may  be  isolated  either  in 
Yi  alcohol  or,  according  to  R.  Heidenhain  (83),  in  a  5^  aqueous  solu- 
tion of  neutral  ammonium  Chromate.  The  latter  method  shows  clearly 
the  striation  of  the  epithelium. 

The  autophysiologic  injection  with  indigo-carmin,  applied  as  in  the 
case  of  the  liver,  fills  the  uriniferous  tubules,  which  may  then  be  further 
examined  in  sections. 

The  blood-vessels  are  examined  in  injected  specimens  (injection 
of  the  kidney  is  easily  accomplished).  In  larger  animals  the  injection  is 
made  into  the  renal  artery,  while  in  smaller  ones  the  whole  posterior  half 
of  the  body  is  injected  through  the  abdominal  aorta. 

The  ureter  and  bladder  are  cut  open,  fixed,  and  then  sectioned. 
In  this  way  the  organs  are  shown  in  a  collapsed  condition,  in  which  the 
arrangement  of  the  epithelium  is  totally  different  from  that  found  in  the 
distended  organs.  In  order  to  observe  them  in  the  latter  condition  the  fix- 
ing agent  is  injected  into  the  ureter  or  bladder,  when,  after  proper  liga- 
tion, they  are  placed  in  the  same  fixing  agent. 

The  usual  fixing  fluids  are  employed  in  the  demonstration  of  the 
suprarenal  capsule;  but  mixtures  containing  chromic  acid,  whether 
Flemming's  fluid,  chromic  acid,  or  its  salts,  are  of  special  importance  in 
the  examination  of  the  organ,  since  the  medullary  substance  of  the  supra- 
renal capsule  stains  a  specific  brown  when  treated  by  these  mixtures  (a  con- 
dition only  reduplicated  in  certain  cells  of  the  hypophysis).  This  brown 
staining  also  occurs  when  the  cortical  and  medullary  portions  are  entirely 
separated,  as  is  the  case  in  certain  animals  and  during  the  development 
of  the  suprarenal  capsule.  The  fat  found  in  the  cells  of  the  suprarenal 
cortex  is  not  identical  with  that  of  the  rest  of  the  body,  as  it  may  be  dis- 
solved by  chloroform  and  oil  of  bergamot  out  of  tissue  fixed  with  osmic 
acid  (Hans  Rabl). 


344  THE    GENITO-URINARY    ORGANS. 

C  THE  FEMALE  GENITAL  ORGANS. 

U  THE  OVUM. 

The  product  of  the  ovaries  is  the  matured  "  ovum,"  or  egg,  hav- 
ing a  diameter  of  from  0.22  to  0.32  mm.  It  forms  a  single  cell 
with  a  thick  membrane,  from  7/1  to  1 1  /^  in  thickness,  known  as 
the  zona  pellucida.  The  ovum  consists  of  a  cell-body  known  as 
the  yolk  or  vitellus,  and  a  nucleus,  from  30//  to  40  jut  in  diameter, 
termed  the  germinal  vesicle.  The  vitellus  consists  of  two  sub- 
stances— a  protoplasmic  network,  with  a  somewhat  denser  arrange- 
ment at  the  periphery  of  the  cell  and  in  the  neighborhood  of  the 
germinal  vesicle,  and  of  small,  highly  refractive,  and  mostly  oval 
bodies  imbedded  between  the  meshes  of  the  protoplasm — the  yolk 
globules.  These  latter,  as  a  rule,  are  merely  browned  on  being 
treated  with  osmic  acid,  although  occasionally  a  true  fatty  reaction 
may  be  obtained.  The  germinal  vesicle  is  surrounded  by  a  distinct 
membrane  having  a  double  contour.  In  its  interior  we  find  a 
scanty  lining  framework  containing  very  little  chromatin,  and  one  or 
two  relatively  large  false  nucleoli,  or  germinal  spots,  from  y/j,  to  lo// 
in  diameter,  due  to  a  nodal  thickening  of  the  chromatin.  In  the 
latter  a  further  very  distinct  differentiation  is  sometimes  seen  in  the 
shape  of  a  small  body  (vacuole  ?)  of  doubtful  origin,  which  has 
been  called  Schrön's  granule.  The  germinal  vesicle  and  spot  were 
formerly  known  as  "  Purkinje' s  vesicle"  and  "Wagner's  spot," 
respectively,  from  their  discoverers. 

2.  THE  OVARY. 

The  ovaries  are  almost  entirely  covered  by  peritoneum.  The 
mesothelial  cells  of  the  latter,  however,  undergo  here  a  differentia- 
tion, to  form  the  germinal  epithelium.  At  the  hilum  the  peritoneal 
covering  is  absent,  and  it  is  here  that  the  connective-tissue  elements 
of  the  ovarian  ligament  penetrate  into  the  organ  to  form  its  con- 
nective-tissue framework,  the  so-called  stroma  of  the  ovary.  At  an 
early  period  in  the  development  of  the  o\/aries,  the  germinal  epithe- 
lium begins  a  process  of  invagination  into  the  stroma  of  the  ovary, 
so  that  at  the  periphery  of  the  organ  a  zone  is  soon  formed  which 
consists  of  both  connective  tissue  and  epithelial  (mesothelial)  ele- 
ments. This  zone  is  called  the  cortex,  or  parenchymatous  zone. 
That  portion  of  the  organ  in  the  neighborhood  of  the  hilum  (aside 
from  the  rudimentary  structure  known  as  the  epoophoron)  consists 
of  connective  tissue  containing  numerous  elastic  fibers  and  unstriped 
muscle-cells,  and  is  known  as  the  incditUary  substance,  or  vascular 
zone.  This  connective  tissue  penetrates  here  and  there  into  the  cor- 
tex, separates  the  epithelial  elements  of  the  latter  from  each  other, 
and  is  in  direct  continuation  with  a  stratum  immediately  beneath  the 
germinal  epithelium,  called  the  tunica  albuginea.  This  latter  layer 
of  connective  tissue  is  generally  distinct  in  the  adult  ovary,  although 


THE    FEMALE    GENITAL    ORGANS. 


345 


its  structure  and  thickness  vary  to  a  considerable  extent.  In  young 
ovaries  it  is  irregular,  but  shows  in  its  highest  development  three 
layers  distinguishable  from  each  other  by  the  different  direction  of 
the  fibers.  In  the  medullary  substance  the  connective-tissue  fibers 
are  long,  in  the  cortex  short,  and  in  the  zone  containing  the  follicles 
(see  below)  are  mingled  with  numerous  connective-tissue  cells. 
Nonstriated  muscle-fibers  occur  exclusively  in  the  medulla.  Here 
they  are  gathered  in  bundles  which  accompany  the  blood-vessels, 
and  may  even  form  sheaths  around  the  latter.  They  are  especially 
prominent  in  mammalia. 

The  germinal  epitheliuni  is   distinguished  from  that  of  the  re- 
maining peritoneum  by  the  greater  height  of  its  cells,  which  are 

Young  follicle  with  ovum. 


Primordial  ova 


Ovum  with  fol 
licularepithe 
Hum. 


Fig.  275. — Section  from  ovary  of  adult  dog.  At  the  right  the  stellate  figure  repre- 
sents a  collapsed  follicle  with  its  contents.  Below  and  at  the  right  are  seen  the  tubules 
of  the  parovarium  (copied  from  Waldeyer). 


cubic  or  even  cylindric  in  shape.  At  an  early  period  in  the  devel- 
opment of  the  ovaries  this  epithelium  pushes  into  the  underlying 
embryonic  connective  tissue  in  solid  projections,  to  form  the  primmy 
egg  tubes  of  Pßüger,  the  cells  of  which  very  soon  begin  to  show 
differentiation.  Some  retain  their  original  characteristics  and  shape, 
while  others  increase  in  size,  become  rounded,  and  develop  into  the 
young  ova.  Those  retaining  their  indifferent  type  become  the  fol- 
licular cells  surrounding  the  Qgg.  This  differentiation  into  ova  and 
follicular  elements  may  even  occur  in  the  germinal  epithelium  itself, 
in  which  case  the  larger  round  cells  are  known  as  the  primitive  or 
primordial  ova.      In  the  further  development  of  the  ovarian  cortex 


34Ö 


THE    GENITO-URINARY    ORGANS. 


the  primitive  egg  tubes  are  penetrated  throughout  by  connective 
tissue,  so  that  each  egg  tube  is  separated  into  a  number  of  irregular 
divisions.  In  this  way  a  number  of  distinct  epithehal  nests  are 
formed,  which  lose  their  continuity  with  the  germinal  epithelium 
and  finally  lie  imbedded  in  the  connective  tissue.  According  to  the 
shape  and  other  characteristics  of  these  epithelial  nests,  we  may 
distinguish  several  different  groups:  (i)  The  primitive  egg  tubes 


Germinal  epi- 

—  thelium. 

T>  Tunica    albu- 
ginea. 

—  Follicular 

.^      epithelium. 
""  Ovum. 


Granular  layer  of 
large  Graafian 
follicle. 


Fig.  276. — From  ovary  of  young  girl ;  X  '9°- 


of  Pflüger ;  (2)  the  typical  primitive  follicles — i  e.,  those  which 
contain  only  a  single  egg-cell  (present  in  the  twenty -eighth  week  of 
fetal  life)  ;  (3)  the  atypic  follicles — i  e.,  those  containing  from  two 
to  three  egg-cells  ;  (4)  the  so-called  nests  of  follicles,  in  which  a 
large  number  of  follicles  possess  only  a  single  connective-tissue  en- 
velope ;  (5)  follicles  of  the  last-named  type  which  may  assume  the 
form  of  an  elongated  tube,  and  which  are  then  known  as  the  con- 


THE    FEMALE    GENITAL    ORGANS.  34/ 

stricted  tubes  of  Pflüger.  The  fourth,  fifth,  and  possibly  the  third 
types  are  further  divided  by  connective-tissue  septa,  until  they 
finally  form  distinct  and  typical  follicles  (Schottländer,  91,  93). 

In  the  adult  ovary  true  Ggg  tubes  are  no  longer  developed. 
Isolated  invaginations  of  the  germinal  epithelium  sometimes  occur, 
but  apparently  lead  merely  to  the  formation  of  epithelial  cysts 
(Schottländer).  The  theories  as  to  when  the  formation  of  new 
epithelial  nests  or  follicles  ceases  are,  however,  very  conflicting, 
some  authors  believing  that  cessation  takes  place  at  birth,  others 
that  it  continues  into  childhood  and  even  into  middle  age. 

The  typical  primitive  follicle  consists  of  a  relatively  large  egg- 
cell  surrounded  by  a  single  layer  of  smaller  cubical  or  cylindri-c 
follicular  cells.  The  growth  of  the  follicle  takes  place  by  means 
of  mitotic  division  in  the  follicular  cells  and  increase  in  size  of 
the  ovum.  The  egg-cell  is  soon  surrounded  by  several  layers  of 
cells,  and  gradually  assumes  an  eccentric  position  in  the  cell 
complex.  At  a  certain  distance  from  the  ovum  and  nearly  in  the 
center  of  the  follicle  one  or  more  cavities  form  in  the  follicular 
epithelium.  These  become  confluent,  and  the  resulting  space  is 
filled  by  a  fluid  derived,  on  the  one  hand,  from  a  process  of 
secretion  and,  on  the  other  hand,  from  the  destruction  of  some 
of  the  follicular  cells.  The  cavity  is  called  the  antrum  of  the 
follicle,  and  such  a  follicle  has  received  the  name  of  Graafian 
follicle.  Its  diameter  varies  from  0.5  to  6  mm.  The  follicle  in- 
creases in  size  through  cell-proliferation,  the  cavity  increasing  and 
gradually  inclosing  the  Q.gg  together  with  the  follicular  cells  imme- 
diately surrounding  it,  although  the  latter  always  remain  connected 
with  the  wall  of  the  vesicle  at  some  point.  The  &gg  now  lies 
imbedded  in  a  cell-mass,  the  discus  proligcj-ns,  which  is  composed 
of  follicular  epithelium,  and  projects  into  the  follicular  cavity. 
The  follicular  epithelium  forming  the  wall  of  the  cavity  is  known  as 
the  straUini  gramilostim,  the  cavity  as  the  antrum,  and  the  fluid 
which  it  contains  as  the  liquor  folliculi.  Those  follicular  cells 
which  immediately  surround  and  rest  upon  the  ovum  are  some- 
what higher  than  the  rest  and  constitute  the  &gg  epithelium,  or 
corona  radiata. 

During  the  growth  of  the  follicle  the  connective  tissue  surround- 
ing it  becomes  differentiated  into  a  special  envelope,  called  the  thcca 
folliculi.  In  it  two  layers  may  be  distinguished — the  outer,  the 
tunica  externa,  consisting  of  fibrous  connective  tissue,  is  continu- 
ous with  the  inner,  or  tunica  interna,  rich  in  blood-vessels  and 
cellular  elements.  The  follicle  gradually  extends  to  the  surface  of 
the  ovary,  at  which  point  it  finally  bursts  (see  below),  allowing  the 
ovum  to  escape  into  the  body  cavity  and  thus  into  the  oviduct. 

During  the  growth  and  development  of  the  ovarian  follicles  the 
ova  undergo  certain  changes  of  size  and  structure  which  may  receive 
further  consideration.  These  have  been  described  for  the  human 
ovary  by  Nagel  (96),  whose  account  will  here  be  followed.     The 


Fig.  280. 

Figs.  277,  278,  279,  and  280. — From  sections  of  cat's  ovary,  showing  ova  and 
follicles  in  different  stages  of  development  ;  X  225  :  a,  a,  a,  a,  Germinal  spots  ;  h,  b,  b,  b, 
germinal  vesicles  ;  c,  c,  c,  c,  ova  ;  d,  d,  d,  zonse  pellucidse  ;  e,  e,  e,  e,  corona  radiata  ; 
f,  f,  f,  f,  tbecse  folliculorum  ;   g,  beginning  of  formation  of  the  cavity  of  the  follicle. 

348 


THE  FEMALE  GENITAL  ORGANS. 


349 


ova  of  the  primitive  or  primordial  follicles  attain  a  size  (in  fresh  tissue 
teased  in  normal  salt  solution)  varying  from  48 //  to  69//.  They 
possess  a  nucleus  varying  in  size  from  20//  to  32 /i,  presenting  a 
doubly  contoured  nuclear  membrane,  and  containing  a  distinct 
chromatin  network  with  a  nucleolus  and  several  accessory  nucleoli. 
The  protoplasm  shows  a  distinct  spongioplastic  network  containing 
a  clear  hyaloplasm.  The  primitive  ova,  until  they  undergo  further 
development,  retain  this  size  and  structure,  irrespective  of  the  age 
of  the  individual.  They  are  numerous  in  embryonic  life  and  early 
childhood,    always   found    during    the    ovulation    period,    but    not 


Fig.  281. — Transverse  section  through  the  cortex  of  a  human  ovary  ;  X  5°  •  ^> 
Tunica  albuginea ;  ep,  follicular  epithelium,  zona  granulosa  ;  ^, primordial  follicles  ;  oz', 
ovum  in  the  discus  proligerus  ;  the,  theca  externa  folliculi  ;  thi,  theca  interna  folliculi  with 
blood-vessels  (Sobotta,  "Atlas  and  Epitome  of  Human  Histology"). 


observed  in  the  ovaries  of  the  aged.  Changes  in  the  size  and 
structure  of  the  ova  accompany  the  proliferation  of  the  follicular 
cells  in  the  growing  follicles.  As  soon  as  the  follicular  cells  of  a 
primitive  follicle  proliferate,  as  above  described,  the  ovum  of  the 
follicle  increases  in  size  until  it  has  attained  the  size  of  a  fully 
developed  ovum.  The  zona  pellucida  now  makes  its  appearance, 
and  after  this  has  reached  a  certain  thickness,  yolk  granules  (deuto- 
plastic  granules)  develop  in  the  protoplasm  of  the  ovum.  In  a 
fully  developed  Graafian  follicle  the  ovum  presents  an  outer  clearer 
protoplasmic  zone  and  an  inner  fine  granular  zone  containing  yolk 


350  THE    GENITO-URINARY    ORGANS. 

granules ;  in  the  former  lies  the  germinal  vessel.  Between  the 
protoplasm  of  the  ovum  and  the  zona  pellucida  is  found  a  narrow 
space  known  as  the  perivitelline  space.  The  germinal  vesicle 
(nucleus),  which  is  usually  of  spheric  shape,  possesses  a  doubly 
contoured  membrane  and  a  large  germinal  spot  (nucleolus),  which 
shows  ameboid  movements. 

The  origin  of  the  zona  pellucida  has  not  as  yet  been  fully  de- 
termined. It  probably  represents. a  product  of  the  egg  epithelium, 
and  may  be  regarded  in  general  as  a  cuticular  formation  of  these 
cells.  At  all  events  it  contains  numerous  small  canals  or  pores  into 
which  the  processes  of  the  cells  composing  the  corona  radiata  ex- 
tend. These  processes  are  to  be  regarded  as  intercellular  bridges 
(Retzius,  90) ;  and,  according  to  Palladino,  they  occur  not  only 
between  the  ovum  and  the  corona  radiata,  but  also  between  the 
follicular  cells  themselves.  In  the  ripe  human  ovum  the  pores  are 
apparently  absent  (Nagel),  and  it  is  very  probable  that  they  have  to 
do  with  the  passage  of  nourishment  to  the  growing  egg.  Retzius 
believes  that  the  zona  pellucida  is  derived  from  the  processes  of  the 
cells  composing  the  corona  radiata,  which  at  first  interlace  and  form 
a  network  around  the  ovum.  Later,  the  matrix  of  the  membrane  is 
deposited  in  the  meshes  of  the  network,  very  probably  by  the  egg 
itself. 

Further  developmental  changes  are,  however,  necessary  before  a 
fully  developed  ovum  (ripe  ovum)  may  be  fertilized.  These  are 
grouped  under  the  head  of  maturation  of  the  ovum.  They  have  in 
part  been  described  in  a  former  section  (p.  71),  but  may  receive 
further  consideration  at  this  time.  During  maturation  the  chromo- 
somes are  reduced  in  number,  so  that  the  matured  ovum  presents 
only  half  the  number  found  in  a  somatic  cell  of  the  same  animal. 
The  manner  in  which  this  reduction  takes  place  has  been  described 
for  many  invertebrates  and  vertebrates,  and  in  all  ova  studied  with 
reference  to  this  point  essentially  the  same  phenomena  have  been 
observed.  In  this  account  we  shall  follow  the  process  as  it  occurs 
in  the  Copepoda  (Rückert,  94). 

During  the  period  of  growth  the  cells  composing  the  last  gen- 
eration of  oogonia  (primitive  ova)  increase  in  size,  and  are  then 
known  as  "oocytes"  (the  ripe  ova).  These  then  undergo  mitotic 
division,  and  in  each  a  spirem  is  formed  which  divides  into  1 2 
chromosomes,  and  not  into  24  as  in  the  case  of  the  somatic  cells. 
These  12  chromosomes  split  longitudinally,  so  that  the  germinal 
vesicle  is  seen  to  contain  12  pairs  of  chromosomes,  or  daughter 
loops.  By  this  process  the  oogonia  have  become  egg  mother  cells 
(O.  Hertwig,  90)  or  oocytes  of  the  first  order.  The  loops  now 
begin  to  shorten  and  each  soon  divides  crosswise  into  two  equal 
rods,  thus  giving  rise  to  1 2  groups  of  4  chromosomes,  or  1 2  tetrads. 
The  mother  cell  now  divides  into  2  unequal  parts,  the  process  con- 
sisting in  a  distribution  of  the  rods  composing  the  tetrads  in  such  a 


THE    FEMALE    GENITAL    ORGANS. 


351 


way  that  the  pairs  of  rods  derived  from  one  set  of  daughter  loops 
pass  to  the  one  daughter  cell,  and  those  derived  from  the  other  set 
to  the  second  daughter  cell.  In  this  manner  are  formed  the  large 
egg  daughter  cells  (O.  Hertwig)  or  oocytes  of  the  second  order,  and 
a  smaller  cell,  the  first  polar  body.  From  this  it  is  seen  that  the 
daughter  cell  still  retains  12  pairs  of  rods,  A  second  unequal  division 
immediately  follows  without  a  period  of  rest,  but  in  this  case  the  corn- 


Fig.  282. — Schematic  representation  of  the  behavior  of  the  chromatin  during  the 
maturation  of  the  ovum  (from  Riickert,  94).  Instead  of  12  chromosomes  we  have  drawn, 
for  the  sake  of  simpUcity,  only  four :     a,  a,  a,  First,  and  (d)  second  polar  body. 


ponent  parts  of  the  pairs  of  rods  are  so  divided  that  each  separate 
rod  moves  away  from  its  fellow,  although  they  both  originated  from 
the  same  daughter  loop.  In  this  manner  a  cell  of  the  third  gen- 
eration is  formed,  the  oocyte  of  the  third  order,  or  mature  ovum, 
as  well  as  a  second  polar  body.  The  second  division  in  the  period 
of  maturation  is  peculiar  in  that  here  daughter  chromosomes  are 


352  THE    GENITO-URINARY    ORGANS. 

formed,  not  by  a  longitudinal  splitting  of  the  chromosomes,  but  by 
a  transverse  division. 

In  the  process  of  development  of  the  ova,  three  periods  are 
therefore  distinguishable.  The  first,  or  period  of  proliferation,  rep- 
resents a  stage  of  repeated  mitotic  division  in  the  oogonia,  during 
which  the  latter  become  gradually  reduced  in  size.  In  the  second, 
or  period  of  growth,  the  oogonia  increase  in  size  and  are  then  ready 
for  the  third,  or  period  of  maturation.  In  the  latter,  by  means  of 
a  modified  double  mitotic  division,  uninterrupted  by  any  resting 
stage,  the  matured  ovum  and  the  polar  bodies  are  formed.  These 
several  periods  are  represented  in  figure  283. 

The    manner    in   which    the   fully  developed    Graafian    follicle 

Primordial  egg-cell. 


Germinal  zone. 


Oogonia  'Z  /      \  \      \  1     ^T^e  number  of  genera- 

^~--  /         1  /  \  t      tions  IS  much  larger  than 


Zone  of  mitotic  division. 

(The  number  of  ge 
tions  is  much  largei 
here  represented.) 


Oocyte  I.  order. 


I 


Zone  of  growth. 


Oocyte  II.  order. ^^^|  »^    I.   P.B.      ^ Zone  of  maturation. 

Matured  ovum. 


II.   P.B. 


Fig.  283. — Scheme  of  the  development  and  maturation  of  an  ascaris  ovum  (after  Boveri) : 
P.  B.,  Polar  bodies.     (From  "  Ergebn.  d.  Anat.  u.  Entw.,"  Bd.  I.) 


bursts  and  its  ovum  is  freed  is  still  a  subject  of  controversy  ;  the 
following  may  be  said  regarding  it :  By  a  softening  of  the  cells 
forming  the  pedicle  of  the  discus  proligerus,  the  latter,  together 
with  the  ovum,  are  separated  from  the  remaining  granulosa,  and  lie 
free  in  the  liquor  folliculi.  At  the  point  where  the  follicle  comes  in 
contact  with  the  tunica  albuginea  of  the  ovary,  the  latter,  with  the 
theca  folliculi,  becomes  thin,  and  in  this  region,  known  as  the 
stigma,  the  blood-vessels  are  obliterated  and  the  entire  tissue  grad- 
ually atrophies  ;  thus  a  point  of  least  resistance  is  formed  which  gives 
way  at  the  slightest  increase  in  pressure  within  the  follicle,  or  in  its 
neighborhood. 


THE    FEMALE    GENITAL    ORGANS.  353 

The  part  of  the  Graafian  folhcle  which  remains  after  the  ovijm  has 
been  released  forms  a  structure  known  as  the  coj'ptis  lutetivi,  a  struc- 
ture which  passes  through  certain  developmental  stages  and  then 
undergoes  degeneration.  The  regressive  metamorphosis  is  much 
slower  in  a  corpus  luteum  whose  ovum  has  been  fertilized  and  is  in 
process  of  further  development  than  in  those  whose  ova  have  not  been 
impregnated  ;  the  former  is  known  as  the  corpus  luteum,  verum,  the 
latteras  the  corpora  lutea  spuria.  There  is  as  yet  difference  of  opinion 
as  to  the  mode  of  development  of  the  corpora  lutea,  certain  observers 
maintaining  that  the  cells  of  the  zona  granulosa  contribute  largely  to 
the  development  of  these  structures,  while  others  trace  their  origin  to 
the  cells  of  the  theca  interna.  In  this  account  we  shall  follow  Sobotta, 
whose  careful  observations  on  the  development  of  the  corpora  lutea  of 
the  mouse  and  rabbit  support  strongly  the  former  view.  According 
to  this  observer,  the  walls  of  the  Graafian  follicle  collapse  after  its  rup- 
ture. The  cells  of  the  follicular  epithelium,  which  remains  within 
the  collapsed  follicle,  hypertrophy,  the  cells  attaining  many  times  their 
original  size.  As  the  epithelial  cells  enlarge,  a  yellowish  pigment 
known  as  lutein  makes  its  appearance.  The  cells  are  now  designated 
as  lutein  cells.  At  the  same  time  the  vascular  connective  tissue  of  the 
inner  thecal  layer  penetrates  between  the  hypertrophied  epithelial  cells 
in  the  shape  of  processes  accompanied  by  leucocytes. 

The  structure  which  thus  develops  is  known  as  the  corpus 
luteum.  On  the  rupture  of  the  follicle  hemorrhages  often  take 
place  on  account  of  the  laceration  of  the  blood-vessels.  The  re- 
mains of  such  hemorrhages  are  found  in  the  form  of  hematoidin 
crystals. 

After  a  variable  time  the  corpora  lutea  degenerate  ;  in  this  regres- 
sive metamorphosis  the  epithelial  cells  (lutein  cells)  undergo  fatty 
degeneration,  and  the  connective  tissue  trabeculas  become  atrophied. 
Each  corpus  luteum  is  thus  changed  into  a  corpus  albicans,  which  in 
turn  is  absorbed,  and  in  its  place  there  remains  only  a  connective 
tissue  containing  very  few  fibers. 

Not  all  of  the  eggs  and  follicles  reach  maturity  ;  very  many 
are  destroyed  b)'-  a  regressive  process  known  as  atresia  of  the  fol- 
licles. This  process  may  begin  at  any  stage,  even  affecting  the 
primitive  ova  while  still  imbedded  in  the  germinal  epithelium — first 
attacking  the  ^^g  itself  and  later  the  surrounding  follicular  epithe- 
lium, although  in  both  the  degenerative  process  is  identical.  The 
germina?!  vesicle  and  the  nuclei  of  the  follicular  cells  usually 
undergo  a  chromatolytic  degeneration,  although  they  sometimes 
disappear  without  apparent  chromatolysis  (direct  atrophy),  while 
the  cell-bodies  are  generally  subjected  to  a  fatty  degeneration  or 
may  even  undergo  what  is  known  among  pathologists  as  an  albu- 
minous degeneration — /.  e.,  one  characterized  by  granulation  and 
showing  no  fat  reaction  but  numerous  reactions  such  as  are  ob- 
served where  albumin  is  present.  These  two  forms  of  metamor- 
23 


354  THE    GENITO-URINARY    ORoANS. 

phosis  result  in  a  liquefaction  of  the  cell-body,  and  finally  lead  to 
a  hyaline  swelling,  which  renders  the  substance  of  the  cell  homo- 
geneous. The  zona  pellucida  softens,  increases  in  volume,  becomes 
wrinkled,  and  after  some  time  is  absorbed,  A  further  stage  in 
the  regressive  process  consists  in  the  formation  of  scar  tissue,  as 
in  the  case  of  the  corpus  luteum.  Here  leucocytes  accompany 
the  proliferation  from  the  tunica  interna  of  the  theca  folliculi,  and 
assist  in  absorbing  the  products  of  degeneration,  the  result  being 
a  connective-tissue  scar  {vid.  G.  Ruge,  and  Schottländer,  91,  93). 

The  blood-vessels  of  the  ovary  enter  at  the  hilum  and  branch 
in  the  medullary  substance  of  the  ovary.  From  these  medullary 
vessels  branches  are  given  off  which  penetrate  the  follicular  zone, 
giving  off  branches  to  the  follicles  and  terminating  in  a  capillary 
network  in  the  tunica  albuginea  (Clark,  1900).  The  relations  of 
the  branches  to  the  follicles  are  such  that  in  the  outer  layer  of  the 
theca  folliculi  the  vessels  form  a  network  with  wide  meshes  while 
the  inner  layer  contains  a  fine  capillary  network.  The  veins  are  of 
large  caliber  and  form  a  plexus  at  the  hilum  of  the  ovary. 

The  lymphatics  of  the  ovary  are  numerous.  They  begin  in 
clefts  in  the  folhcular  zone,  which  unite  to  form  vessels  lined  by 
endothelial  cells  in  the  medulla.  They  leave  the  ovary  at  the 
hilum. 

The  nerves  accompany  and  surround  the  blood-vessels,  while 
very  few  nerve-fibers  penetrate  into  the  theca  folliculi ;  those  doing 
so  form  a  network  around  the  follicle  and  end  often  in  small  nodules 
without  penetrating  beyond  the  theca  itself  Ganglion  cells  of  the 
sympathetic  type  also  occur  in  the  medulla  of  the  ovary  near  the 
hilum  (Retzius,  93 ;   Riese,  Gawronsky). 

3.  THE  FALLOPIAN  TUBES,  UTERUS,  AND  VAGINA. 

The  Fallopian  tubes  or  ova  ducts  consist  of  a  mucous  mem- 
brane, muscular  coat,  and  peritoneal  covering. 

The  mucous  membrane  presents  a  large  number  of  longitudinal 
folds  which  present  numerous  secondary  folds  which  frequently 
communicate  with  one  another.  Very  early  in  the  development 
four  of  these  folds  are  particularly  noticeable  in  the  isthmus ;  these 
may  also  be  recognized  at  times  in  the  adult.  These  are  the 
chief  folds,  in  contradistinction  to  the  rest,  which  are  known  as 
the  accessory  folds  (Frommel).  The  accessory  folds  are  well 
developed  in  the  isthmus,  and  are  here  so  closely  arranged  that 
no  lumen  can  be  seen  with  the  naked  eye.  The  epithelium 
lining  the  tubes  is  composed  of  a  single  layer  of  ciliated  columnar 
cells  which  entirely  cover  the  folds  as  well  as  the  tissue  between 
them.  Glands  do  not  occur  in  the  oviducts,  unless  the  crypts 
between  the  folds  may  be  considered  as  such.  The  mucosa 
beneath   the   epithelium  contains    relatively   few    connective-tissue 


THE    FEMALE    GENITAL    ORGANS. 


355 


fibers,  but  numerous  cellular  elements.  In  the  isthmus  it  is  com- 
pact, but  in  the  ampulla  and  infundibulum  its  structure  is  looser. 
The  mucosa  contains  a  few  nonstriated  muscle-fibers,  which  have  a 
longitudinal  direction  and  extend  into  the  chief  folds,  but  not  into 
the  accessory  folds. 

External  to  the  mucosa  is  found  the  muscular  coat,  consisting 
of  an  inner  circular  and  an  outer  and  thinner  longitudinal  layer 
consisting  of  bundles  of  nonstriated  muscular  tissue  separated  by 
connective  tissue  and  blood-vessels.  The  longitudinal  layer  is  im- 
perfectly developed  in  the  ampulla  and  may  be  entirely  absent  in 
the  infundibulum.  The  peritoneal  layer  consists  of  a  loose  connec- 
tive tissue  covered  by  mesothelium. 


Mucosa. 


Crypt 


Fig.   284.  — Section  of  oviduct  of  young  woman.     To  the  left  and  above  are  two 
enlarged  ciliated  epithelial  cells  from  the  same  tube  ;  X  I70- 


The  ova  ducts  have  a  rich  blood-supply.  The  terminal  branches 
of  the  arteries  pass  into  the  primary  and  secondary  folds  of  the 
mucosa,  where  they  form  capillary  plexuses  under  the  epithelium. 
The  blood  is  returned  by  means  of  a  well-developed  venous  plexus. 
The  lymphatic  vessels  have  their  origins  in  the  folds  of  the  mucosa. 
Nerve-fibers  have  been  traced  to  the  musculature  and  to  the  lining 
epithelial  cells. 

The  uterus  is  composed  of  a  mucous,  a  muscular,,  and  a  peri- 
toneal coat. 

The  mucosa  of  the  body  of  the  uterus  and  cervix  is  lined  by  a 
single  layer  of  columnar  ciliated  epithelial  cells  ;  these  are  some- 


356  THE    GENITO-URINARY    ORGANS. 

what  higher  in  the  cervix  than  in  the  corpus.  Barfurth  (96)  has 
found  intercellular  bridges  between  the  cells  of  the  uterine  epithelium 
in  the  guinea-pig  and  rabbit.  In  the  cervix  of  the  virgin  the  cihated 
columnar  epithelium  extends  as  far  as  the  external  os,  at  which 
point  this  usually  changes  to  a  stratified  squamous  epithelium.  In 
multiparas  the  squamous  epithelium  extends  into  the  cervical  canal 
and  may  be  found,  with  occasional  exceptions  (islands  of  ciliated 
epithelium),  throughout  its  entire  lower  third.  This  arrangement 
is  subject  to  considerable  variation,  so  that  even  in  children  the 
lower  portion  of  the  cervical  canal  may  sometimes  be  lined  by 
stratified  epithelium.  Recent  investigations  have  established  the 
fact  that  in  both  the  uterus  and  oviducts  the  general  direction  of  the 
wave-like  ciliary  motion  is  toward  the  vagina  (Hofmeier).  In  the 
body  of  the  uterus  the  mucosa  is  composed  of  a  reticular  connective 
tissue  consisting  of  relatively  few  connective-tissue  fibers  and  branched 
connective-tissue  cells  arranged  in  the  form  of  a  network,  in  the 
meshes  of  which  are  found  lymphocytes  and  leucocytes.  Under 
low  magnification  the  mucosa  presents  more  the  appearance  of 
adenoid  tissue  than  of  areolar  connective  tissue.  The  mucosa  of 
the  cervix  is  somewhat  denser,  containing  more  fibrous  tissue.  In 
the  cervical  canal  the  mucosa  of  the  anterior  and  posterior  walls  is 
elevated  to  form  numerous  folds,  extending  laterally  from  larger 
median  folds.      These  folds  are  known  as  the  pliccE  palmatcB. 

The  mucosa  of  the  body  of  the  uterus  and  of  the  cervix  contains 
numerous  glands,  the  uterine  and  cervical  glands.  The  uterine 
glands  are  branched  tubular  in  type,  and  extend  through  the  mucosa 
and  certain  ones  may  even  extend  for  a  short,  distance  into  the 
muscular  layer.  They  are  lined  by  ciliated  columnar  epithelium, 
resting  on  a  basement  membrane.  The  cervical  glands  are  larger 
and  more  branched  than  those  of  the  body  of  the  uterus,  and  belong 
to  the  type  of  tubulo-alveolar  glands  ;  they  have  a  mucous  secretion. 
The  glands  and  crypts  extend  as  far  as  the  external  os.  In  the 
mucous  membrane  of  the  cervical  region  we  find  peculiar  closed 
sacs  of  varying  size  lined  by  simple  cylindric  epithelium,  the  so- 
called  ovida  NabotJii,  which  probably  represent  cystic  formations 
{vid.  A.  Martin). 

Three  layers  of  muscular  tissue  are  to  be  seen  both  in  the 
corpus  and  cervix  uteri — an  inner  longitudinal,  a  middle  nearly  cir- 
cular, in  which  the  principal  blood-vessels  are  found,  and  an  outer 
longitudinal.  The  inner  and  outer  layers  are  known  respectively 
from  their  position  as  the  stratum  mucosum  and  stratum  serosum, 
the  middle  and  more  vascular  as  the  stratum  vasculosum.  As  com- 
pared with  the  middle,  the  inner  and  outer  muscle  layers  are 
poorly  developed.  The  complicated  conditions  found  in  the  uterine 
musculature  can  be  better  understood  if  some  attention  be  paid  to 
its  origin.  The  circular  layer  should  be  regarded  as  the  original 
musculature  of  the  Müllerian  ducts.  The  outer  longitudinal  layer 
develops  later,  and  is  derived  from  the  musculature  of  the  broad 


THE    FEMALE    GENITAL    ORGANS. 


357 


ligament.  Between  these  two  are  the  large  vessels  accompanied 
by  a  certain  amount  of  muscular  tissue — a  condition  which  persists 
throughout  life  in  the  Carnivora.  In  man  the  blood-vessels  pene- 
trate into  the  circular  musculature  and  only  appear  later  in  the 
inner  muscular  layer.  A  true  muscularis  mucosae  is  not  present  in 
the  human  uterus  (Sobotta,  91). 

The  serous  or  peritoneal  layer  consists  of  a  layer  of  mesothelial 
cells  and  submesothelial  connective  tissue. 

The  uterus  derives  its  blood  supply  from  the  uterine  and  ovarian 
arteries,  which  enter  from  the  broad  ligament  through  its  lateral 
portion.  These  vessels  pass  to  the  stratum  vasculosum  of  the 
muscular  layer,  where  they  branch  repeatedly,  some  of  the  branches 


>-    Mucosa. 


i^^j^^. 


- ;  ;^^>  ^'-*'^*;''Ä«(««wA*;^:>»*^  ;^«;m^*^«bw» 


Fig.  285. — From  uterus  of  young  woman ;   X  34-      (From  a  preparation  by  Dr. 

J.  Amann.) 


entering  the  mucosa,  where  they  form  ca,pillary  networks  surround- 
ing the  glands  and  a  dense  capillary  network  situated  under  the 
uterine  epithelium.  The  veins  form  a  venous  plexus  in  the  deeper 
portion  of  the  mucosa,  especially  well  developed  in  the  cervix  and 
OS  uteri.  From  this  plexus  the  blood  passes  to  a  second  well- 
developed  venous  plexus  situated  in  the  stratum  vasculosum  of  the 
muscular  layer,  whence  the  blood  passes  to  the  plexus  of  uterine 
and  ovarian  veins. 

The  lymphatics  begin  in  numerous  clefts  in  the  uterine  mucosa ; 


358 


THE    GENITO- URINARY    ORGANS. 


from  here  the  lymph  passes  by  way  of  lymph-vessels  to  the  mus- 
cular coat,  between  the  bundles  of  which  are  found  numerous 
lymph-vessels  especially  in  the  middle  or  vascular  layer.  These 
lymph-vessels  terminate  in  larger  vessels  found  in  the  subserous 
connective  tissue. 

The  uterus  receives  numerous  medullated  and  nonmedullated 
nerves.  The  latter  terminate  in  the  muscular  layers.  Medullated 
fibers  have  been  traced  into  the  mucosa,  where  they  form  plexuses 
under  the  epithelium,  from  which  branches  have  been  traced 
between  the  epithelial  cells  and  between  the  gland  cells.  In  the 
course  of  the  nerves  ganglion  cells  of  the  sympathetic  type  have 
been  observed. 


'  -^'1  ■p'' 


uw 


Fig.  286. — From  section  of  human  vagina. 


In  the  vagina  we  distinguish  also  three  coats — the  mucous 
membrane,  the  muscular  layer,  and  the  outer  fibrous  covering. 

The  epithelium  of  the  mucous  membrane  is  of  the  stratified 
squamous  type,  and  possesses,  as  usual,  a  basal  layer  of  cylindric 
cells.  The  mucosa  of  the  vagina  consists  of  numerous  connective- 
tissue  fibers  mingled  with  a  number  of  exceptionally  coarse  elastic 
fibers.  Papillae  containing  blood-vessels  are  present  everywhere  ex- 
cept in  the  depressions  between  the  columnae  rugarum.  It  is  generally 
stated  that  the  vagina  has  no  glands,  but  according  to  the  observa- 
tions of  von  Preuschen  and  C.  Ruge,  a  few  isolated  glands  occur  in 


THE    FEMALE    GENITAL    ORGANS. 


359 


the  vagina.  They  are  relatively  simple  in  structure,  form  irregular 
tubes,  and  are  lined  by  ciliated  columnar  epithelium.  The  excre- 
tory ducts  are  lined  by  stratified  squamous  epithelium.  Diffuse 
adenoid  tissue  is  met  with  in  the  mucosa,  which  sometimes  assumes 
the  form  of  lymphatic  nodules. 

The  muscular  coat,  which  in  the  lower  region  is  quite  prominent, 
may  be  separated  indistinctly  into  an  outer  longitudinal  and  an  in- 
ner circular  layer  ;  the  latter  is,  as  a  rule,  poorly  developed,  and  may 
be  entirely  absent.  The  muscular  coat  is  especially  well  developed 
anteriorly  in  the  neighborhood  of  the  bladder. 


Fig.  287. — From  section  of  human  labia  minora. 


The  outer  fibrous  layer  consists  of  dense  connective  tissue 
loosely  connected  with  the  adjacent  structures. 

At  its  lower  end  the  vagina  is  partially  closed  by  the  hymen 
which  must  be  regarded  as  a  rudiment  of  the  membrane  which  in 
the  embryo  separates  the  lower  segment  of  the  united  Müllerian 
ducts  from  the  ectoderm  of  the  sinus  urogenitalis.  Accordingly, 
the  epithelium  on  the  inner  surface  of  the  hymen  partakes  of  the 
character  of  the  vaginal  epithelium  ;  that  on  the  outer  surface  re- 
sembling the  skin  in  structure  (G.  Klein). 


360  THE    GENITO-URINARY    ORGANS. 

The  epithelium  of  the  vestibulum  gradually  assumes  the  char- 
acteristics of  the  epidermis ;  its  outer  cells  lose  their  nuclei  and 
sebaceous  glands  occur  here  and  there  in  the  neighborhood  of  the 
urethral  orifice  and  on  the  labia  minora.  Hair  begins  to  appear  on 
the  outer  surface  of  the  labia  majora. 

The  clitoris  is  covered  by  a  thin  epithelial  layer,  resembhng  the 
epidermis.  This  rests  on  a  fibrous-tissue  mucosa  having  numerous 
papillae,  some  of  which  contain  capillaries,  others  special  nerve- 
endings.  In  the  clitoris  of  the  adult  no  glands  are  found.  The 
greater  portion  of  the  clitoris  consists  of  cavernous  tissue,  homol- 
ogous to  the  corpora  cavernosa  of  the  persis ;  the  corpus  spongi- 
osum is  not  present  in  the  clitoris. 

The  glands  of  BarthoHn,  the  homologues  of  the  glands  of 
Cowper  in  the  male,  are  mucous  glands  situated  in  the  lateral 
walls  of  the  vestibule  of  the  vagina.  The  terminal  portions  of 
their  ducts  are  lined  by  stratified  squamous  epithelium. 

Free  sensory  nerve-endings,  with  or  without  terminal  enlarge- 
ments, have  been  demonstrated  in  the  epithelium  of  the  vagina 
•(Gawronski).  The  sensory  nerve-fibers  form  plexuses  in  the 
mucosa,  and  lose  their  medullary  sheaths  as  they  approach  the 
epithelium.  Sympathetic  ganglia  are  met  with  along  the  course  of 
these  nerves,  and  nonmedullated  nerves  terminate  in  the  involuntary 
muscular  tissue  of  the  vaginal  wall. 

In'the  connective-tissue  papillae  and  in  the  deeper  portions  of  the 
mucosa  of  the  glans  cHtoridis  are  found,  besides  the  ordinary  type 
of  tactile  corpuscles  and  the  spherical  end-bulbs  of  Krause,  the  so- 
called  genital  corpuscles  (see  p.  171).  Numerous  Pacinian  cor- 
puscles have  been  observed  in  close  proximity  to  the  nerve-fibers 
of  the  clitoris  and  the  labia  minora. 


In  varying  regions  of  the  medullary  substance  of  the  ovary, 
but  more  usually  in  the  neighborhood  of  the  hilum,  there  occur 
irregular  epithelial  cords  or  tubules  provided  with  columnar  epithe- 
lium, ciliated  or  nonciliated,  which  constitute  the  paroophoroii. 
These  are  the  remains  of  the  mesonephros,  and  are  continuations 
of  that  rudimentary  organ — the  epoophoron — of  similar  structure 
which  lies  within  the  broad  ligament.  The  separate  tubules  of  the 
epoophoron  communicate  with  the  duct  of  Gärtner  (Wolffian  duct), 
which  in  the  human  being  is  short,  ends  blindly,  and  never,  as  in 
certain  animals,  opens  into  the  lower  portion  of  the  vagina.  These 
derivatives  of  the  primitive  kidney  consist  of  blindly  ending  tubules 
of  varying  length  lined  by  a  ciliated  epithelium,  the  cells  of  which 
are  often  found  in  process  of  degeneration. 

The  hydatids  of  Morgagni  are  duplications  of  the  peritoneum. 


THE    MALE   GENITAL   ORGANS.  36 1 


D.  THE  MALE  GENITAL  ORGANS. 

J.  THE  SPERMATOZOON. 

The  semen,  or  sperma,  is  a  fluid  that,  as  a  whole,  consists  of 
the  secretion  of  several  sets  of  glands  in  which  the  sexual  cells,  the 
spermatosomes,  or  spermatozoa,  which  are  formed  in  the  testes,  are 
suspended. 

We  shall  first  consider  the  structure  of  the  typical  adult  sperma- 
tosome,  taking  up  consecutively  its  component  parts.  Three  prin- 
cipal parts  may  be  distinguished — the  head,  the  middle  piece,  and 
the  tail  or  flagellinn.  The  round  or  oval  body  of  the  head  termi- 
nates in  a  lanceolate  extremity.  The  former  consists  of  chromatin, 
and  is  most  intimately  associated  with  the  phenomenon  of  fertiliza- 
tion. The  middle  piece,  which  is  attached  to  the  posterior  end  of 
the  head,  is  composed  of  a  protoplasmic  envelop  which  surrounds  a 
portion  of  the  so-called  axial  thread.  The  latter  is  enlarged  ante- 
riorly just  behind  the  head  to  form  the  terminal  nodule,  which  fits  into 
a  depression  in  the  head.    From  the  middle  piece  on,  the  axial  thread 


Fig.  288 — Diagram  showing  the  general  characteristics  of  the  spermatozoa  of 
various  vertebrates :  a.  Lance ;  b,  segments  of  the  accessory  thread  ;  c,  accessory 
thread  ;  d,  body  of  the  head  ;  e,  terminal  nodule  ;  f,  middle  piece  ;  g,  marginal  thread  ; 
h,  axial  thread  ;  i,  undulating  membrane  ;  k,  fibrils  of  the  axial  thread  ;  /,  fibrils  of  the 
marginal  thread ;  711,  end  piece  of  Retzius  ;  n,  rudder-membrane. 

is  continued  into  the  tail  of  the  spermatozoon,  and  is  here  sur- 
rounded by  a  transparent  substance — the  sheatJi  of  the  axial  thread. 
The  envelop  is  lacking  at  the  posterior  extremity  of  the  tail,  where 
the  axial  thread  extends  for  a  short  distance  as  a  naked  filament 
called  the  end-piece  of  Retzius.  From  the  middle  piece  a  still  finer 
thread  is  given  off,  the  marginal  thread,  which  extends  at  a  certain 
distance  from  the  axial  thread  as  far.  as  the  end-piece  of  Retzius. 
In  its  course  it  crosses  and  recrosses  the  axial  thread  at  various 
points,  and  may  even  wind  around  it  in  a  spiral  manner.  In  all  in- 
stances it  is  connected  with  the  sheath  of  the  axial  thread  by  a 
delicate  membrane — the  iindidating  membrane.  Another  and  still 
more  delicate  filament — the  accessory  thread — runs  parallel  with  the 
axial  thread  along  the  surface  of  its  sheath  and  terminates  at  a  cer- 
tain distance  from  the  end-piece  of  Retzius.  Near  the  extremity  of 
the  flagellum  and  immediately  in  front  of  the  end-piece  is  another 
and  shorter  membrane, — the  rudder  membrane, — which  is  continu- 
ous with  the   undulating  membrane.      Maceration  reveals  a  fibrillar 


362 


THE    GENITO-URINARY    ORGANS. 


structure  of  both  the  axial  and  marginal  threads  (Ballowitz),  while 
the  accessory  thread  is  separated  into  a  number  of  short  segments. 
In  mammalia,  and  especially  in  man,  the 
spermatozoa  seem  to  be  more  simply  con- 
structed. Here  the  head  is  pyriform,  and 
somewhat  flattened,  with  a  slight  ridge  along 
the  depression  at  either  side  of  its  anterior 
thinner  portion  (Fig.  289).  In  some  mammalia 
(mouse),  the  head  is  provided  with  a  so- 
called  cap,  which  corresponds  to  the  lance 
previously  mentioned.  The  middle  piece  is 
relatively  long  and  shows  a  distinct  cross- 
striation,  which  may  be  attributed  to  its  spiral 
structure.  Here  also  the  middle  piece  is  tra- 
versed by  the  axial  thread,  which  ends  at  the 
head  in  a  terminal  nodule,  and  may  be  sep- 
arated as  in  other  mammalia  into  a  number 
of  fibrils.  Some  years  ago  Gibbes  described 
an  undulating  membrane  in  the  human  sper- 
matozoon, an  observation  which  was  confirmed 
by  W.  Krause  (81).  The  head  of  the  human 
spermatosome  is  from  3  //  to  5  p.  long,  and 
from  2  fj.  to  3  //  in  breadth  ;  the  middle  piece 
is  6  //  long  and  i  //  in  breadth  ;  the  tail  is  from 
at  the  left  after  Retzius     aq  n  to  6o  iJ.  long,  and  the  end-piece  6  «  long-. 

(81);    the  one  at   the      ^     Vu  ^  4--      1  4--i  u 

extreme  left  is  seen  in  The  spcrmatozoa  are  actively  motile,  a  phe- 

profile ;  the  other  in  nomenon  due  to  the  flagella,  which  give  them 
surface  view;   the  one     ^  spiral,  boHng  motion.      They  are   character- 

at  the  riffht  is  drawn  as       .        ,    ,  ,  .  , 

described  by  Jensen:«,  ized  by  great  longevity  and  are  very  resistant 
Head ;  b,  terminal  nod-  to  the  action  of  low  temperatures  {vid.  Pier- 
ule;  r,  middle  piece ;     g^j     g   y       jj^   g^^^  species  of    bat  the    sper- 

a,  tail ;  e,  end-piece  of  <        0/  r  r       i 

Retzius.  matozoa    penetrate    into    the    oviduct    of    the 

female  in  the  fall,  but  do  not  contribute  to  im- 
pregnation until  the  spring,  when  the  ova  mature.  (For  the 
structure  of  the  spermatosomes  see  Jensen,  Ballowitz.) 


Fig.  289. — Human 
spermatozoa.     The  two 


2.  THE  TESTES. 

The  testis  is  inclosed  within  a  dense  fibrous  capsule, — the 
tunica  albiiginea, — about  one-sixteenth  of  an  inch  in  thickness,  and 
surrounded  by  a  closed  serous  sac,  derived  from  the  peritoneum 
during  the  descent  of  the  testes,  and  therefore  lined  by  mesothelial 
cells.  This  serous  sac — the  tunica  vaginalis — consists  of  a  visceral 
layer  attached  to  the  tunica  albuginea,  and  a  parietal  layer  which 
blends  with  the  scrotum.  The  cavity  contains  normally  a  small 
amount  of  serous  fluid.  On  the  inner  surface  of  the  tunica  albuginea 
is  found  a  thin  layer  of  loose  fibrous  tissue  containing  blood-vessels 
— the  ttmica  vasculosa.     The  tunica  albuginea  is  thickened  in  its 


THE    MALE    GENITAL    ORGANS.  363 

posterior  portion  to  form  the  mediastinum  testis,  or  the  corpus 
Highmori,  which  projects  as  a  fibrous-tissue  ridge  for  a  variable 
distance  into  the  substance  of  the  testis.  The  gross  structure  of  the 
testis  is  best  seen  in  a  sagittal  longitudinal  section.  Even  a  low 
magnification  will  show  that  the  testis  is  composed  of  lobules.  These 
are  produced  by  septa  which  extend  into  the  substance  of  the  organ 
and  are  derived  from  the  investing  tunics  of  the  testis  and  diverge  in 
a  radiate  manner  from  the  mediastinum  testis.  The  lobules  are  of 
pyramidal  shape,  with  their  bases  directed  toward  the  capsule  and 
their  apices  toward  the  mediastinum.  They  consist  principally  of 
the  seminiferous  tubules,  whose  transverse,  oblique,  and  longitudinal 


Lobule  of  testis.      Tunica  albuginea. 


^- '^.i  —  Caput  epidi- 

V'   "*        dymidis. 

\Jj  (p  ^^  cc    I      -^       ail 

''      f^  ^ /.^.^    _    Corpus  Highmori 

7--~"Ynr    ~    and  rete  testis. 

f'^^'-^i Blood-vessel. 


'Tubuli  recti. 


— Vas  epidid\midis. 


Fig.   290.— Longitudinal  section  through  human  testis  and  epididymis.     The  light  areas 
between  the  lobules  are  the  fibrous- tissue  septa  of  the  testis ;  X  2. 


sections  may  be  observed  in  sections  of  the  testis.  When  isolated, 
these  tubules  are  seen  to  begin  in  the  testis  as  closed  canals,  which 
are  closely  coiled  upon  each  other  (convoluted  tubules)  and  describe 
a  tortuous  course,  until  they  finally  reach  the  corpus  Highmori. 
Immediately  before  they  reach  the  latter,  the  convoluted  tubules 
change  into  short,  straight  and  narrow  segments — the  straight 
tubules,  or  tubuli  recti.  Within  the  corpus  Highmori,  all  the  straight 
tubules  of  the  testis  unite  to  form  a  tubular  network — the  rete  testis 
(Haller). 

From  this  network  about  fifteen  tubules — the  vasa  cfferentia — 


364 


THE    GENITO-URINARY    ORGANS. 


arise.  The  latter,  at  first  straight,  soon  begin  to  wind  in  such  a  man- 
ner that  the  various  convolutions  of  each  canal  form  an  independent 
system,  invested  by  a  fibrous  sheath  of  its  own — coni  vasculosi 
Halleri.  These  lobules  constitute  the  elements  of  the  globus  major 
of  the  epididymis.  In  cross-section  the  vasa  efferentia  are  seen  to 
be  stellate  in  shape.  The  vasa  efferentia  gradually  unite  to  form 
one  canal — the  vas  epididymidis.  This  is  markedly  convoluted  and 
is  situated  in  the  body  and  tail  of  the  epididymis  itself 

The  epithelium  of  the  convoluted  seminiferous  tubules  consists 
of  sustentacular  cells  (cells  or  columns  of  Sertoli)  and  of  sperma- 
togenic  elements.  The  former  are  high,  cylindric  structures  (see 
below),  the  basilar  surfaces  of  which  are  in  contact.  They  do  not 
form  a  continuous  layer,  but  their  basal  processes  are  interwoven 
to  form   a  superficial   network  surrounding  the  epithelium  of  the 


Fig.  291.  Fig.  292. 

Sustentacular  cells  (cells  of  Sertoli)  of  the  guinea-pig  (chrome-silver  method). 
Figure  291,  surface  view  of  the  seminiferous  tubules  ;  figure  ^92,  profile  view  ;  X  220  : 
a.  Basilar  surface  of  a  cylindric  sustentacular  cell ;  b,  flattened  sustentacular  cell  ;  c,  c, 
depressions  in  the  sustentacular  cells  due  to  pressure  from  the  spermatogenic  cells  ;  i/, 
basilar  portion  of  sustentacular  cells. 

seminiferous  tubules.  (Fig.  292.)  In  the  meshes  of  the  reticulum 
are  deposited  numbers  of  plate-like  cells,  which  lie  in  contact  with 
the  basement  membrane  and  also  represent  sustentacular  elements 
(vid.  Merkel,  71). 

Between  the  sustentacular  cells  are  found  from  four  to  six  rows 
of  cells,  possessing  relatively  large  nuclei,  rich  in  chromatin,  and 
derived  from  cells  of  the  deeper  strata  by  mitotic  cell  division.  The 
epithelium  of  the  convoluted  portion  of  the  seminiferous  tubules  is, 
therefore,  a  stratified  epithelium.  The  cells  of  this  epithelium 
present  various  peculiarities  according  to  their  stage  of  development, 
and  will  be  considered  more  fully  in  discussing  spermatogenesis. 
Externally,  the  walls  of  the  convoluted  tubules  are  limited  by  a 
single  layer  or  several  layers  of  spindle-shaped,  epithelioid  cells.  A 
basement  membrane  is  present,  but  very  thin,  and  in  some  cases 


THE    MALE   GENITAL   ORGANS. 


365 


hardly  capable  of  demonstration.  The  convoluted  tubules  are 
separated  from  each  other  by  a  small  amount  of  connective  tissue, 
in  which,  in  addition  to  the  vessels,  nerves,  etc.,  are  found  peculiar 
groups  of  large  cells  containing  large  nuclei,  and  known  as  interstitial 
cells.  Nothing  definite  is  known  regarding  the  significance  of  these 
cells  ;  but  they  are  probably  remains  of  the  Wolffian  body.  Reinke 
(96)  found  repeatedly  crystalloids  of  problematic  significance  in  the 
interstitial  cells  of  the  normal  testis. 

The  stratified  epithelium  of  the  convoluted  tubules  changes  in 


Fig-   293. — From  section  of  human  testis,  showing  convoluted  seminiferous 

tubules. 


the  tubuh  recti  to  an  epithelium  consisting  of  a  single  layer  of  short 
columnar  or  cubical  cells  resting  on  a  thin  basement  membrane. 

The  canals  of  the  rete  testis  (Haller)  are  lined  by  nonciliated 
epithelium,  which  varies  in  type  from  flat  to  cubical.  Communicat- 
ing with  the  rete  testis  is  a  blind  canal,  the  vas  aberrans  of  the  rete 
testis,  lined  with  ciliated  epithelium. 

The  vasa  efferentia  are  lined  partly  by  ciliated  columnar  and 
partly  by  nonciliated  cubical  epithelium.  The  two  varieties  form 
groups  which  alternate,  giving  rise  to  nonciliated  depressions, 
which    represent  gland-like  structures   (Schaffer,   92),  but   do  not 


366 


THE    GENITO-URINARY    ORGANS. 


cause  corresponding  evaginations  of  the  mucosa.  The  mucosa, 
which  consists  of  fibrous  connective  tissue,  contains  flattened  endo- 
thehoid  cells,  which  resemble  nonstriated  muscle-cells.  The  latter 
are  found  only  at  the  end  of  the  vasa  efferentia,  just  before  reaching 
the  vas  epididymidis. 


Fig.  294. — Section  through  human  vasa  efferentia  :     0,  Glands  ;  b,  ciliated  epithelium  ; 
c,  glandular  structure  ;  d,  connective  tissue. 


^mm 


Fig.  295. — Cross- section  of  vas  epididymidis  of  human  testis. 

The  vas  epididymidis  is  lined  by  stratified  ciliated  columnar 
epithelium,  resting  on  a  thin  mucosa,  outside  of  which  there  is 
found  an  inner  circular  and  an  outer,  though  thin  and  not  continuous, 
longitudinal  layer  of  nonstriated  muscular  tissue. 

An  aberrant  canaliculus  also  communicates  with  the  vas  epi- 
didymidis, and  is  here  known  as  the  vas  aberrans  Halleri.      Num- 


THE    MALE   GENITAL   ORGANS. 


1^7 


bers  of  convoluted  and  blindly  ending  canaliculi  are  frequently 
found  imbedded  in  the  connective  tissue  around  the  epididymis. 
These  constitute  the  paradidymis,  or  organ  of  Giraldes. 

The  blood-vessels  of  the  testis  spread  out  in  the  corpus  High- 
mori  and  in  the  tunica  vasculosa  of  the  connective-tissue  septa  and 
of  the  tunica  albuginea,  their  capillaries  encircling  the  seminal  tu- 
bules in  well-marked  networks. 

The  lymphatic  vessels  begin  in  clefts  in  the  tunica  albuginea  and 
in  the  connective  tissue  between  the  convoluted  tubules.     They  con- 
verge toward  the  corpus 
Highmori      and      pass 
thence    to    the   spermatic 
cord. 

Retzius  (93)  and  Tim- 
ofeew  (94)  have  described 
plexuses  of  nonmedul- 
lated,  varicose  nerve-fibers 
surrounding  the  blood- 
vessels of  the  testis.  From 
such  plexuses  single 
fibers,  or  small  bundles  of 
such,  could  be  traced  to 
the  seminiferous  tubules, 
about  which  they  also 
form  plexuses.  Such 
fibers  have  not  been 
traced  into  the  epithelium 
lining  the  tubules.  In 
the  epididymis  Timofeew 
found  numerous  sympa- 
thetic ganglia,  the  cell- 
bodies  of  the  sympathetic 

neurones  of  which  were  surrounded  by  pericellular  plexuses.  In 
the  wall  of  the  vas  epididymidis  and  the  vasa  efferentia  were  obsei'ved 
numerous  varicose  nerve-fibers,  arranged  in  the  form  of  a  plexus, 
many  of  which  seemed  to  terminate  on  the  nonstriated  muscle  cells 
found  in  these  tubes.  Some  of  the  nerve-fibers  were  traced  into  the 
mucosa,  but  not  into  its  epithehal  lining. 


Fig.  296. — Section  of  dog's  testis  with  in- 
jected blood-vessels  (low  power)  :  a.  Seminifer- 
ous tubule ;  b,  connective-tissue  septum  ;  c,  blood- 
vessel. 


3.  THE  EXCRETORY  DUCTS. 

The  vas  deferens  possesses  a  relatively  thick  muscular  wall,  con- 
sisting of  three  layers,  of  which  the  middle  is  circular  and  the  other 
two  longitudinal.  The  subepithelial  mucosa  is  abundantly  supplied 
with  elastic  fibers  and  presents  longitudinal  folds.  The  lining  epi- 
thelium is  in  part  simple  ciliated  columnar  and  in  part  stratified 
ciliated  columnar,  with  two  rows  of  nuclei.  The  cilia  are,  however, 
often  absent,  beginning  with  the  lower  portion  of  the  vas  epidi- 


368 


THE    GENITO-URINARY    ORGANS. 


dymidis.  According  to  Steiner,  the  epithelium  of  the  vas  deferens 
varies.  It  may  be  provided  with  ciha  in  the  lower  segments,  or  it 
may  even  be  similar  to  that  found  in  the  bladder  and  ureters. 

The  inner  muscular  layer  is  wanting  in  the  ampulla  of  the  vas 
deferens  ;  here  the  epithelium  is  mostly  simple  columnar  and  pig- 
mented. Besides  the  folds,  there  are  also  evaginations  and  tubules 
which  sometimes  form  anastomoses — structures  which  may  be  re- 
garded as  glands. 

The  seudjtal  vesicles  are  also  lined,  at  least  when  in  a  distended 
condition,  by  simple,  nonciliated  columnar  epithelium  containing 
yellow  pigment.  In  a  collapsed  condition  the  epithelium  is  pseudo- 
stratified,  with  two  or  even  three  layers  of  nuclei.  The  arrange- 
ment of  the  epithelial  cells  in  a  single  layer  would  therefore  seem 
to   be  the   result  of  distention.      The  mucous  membrane   shows 


Epithelium. 


.  _    Inner  longi- 

.^j/^-Jr-'  tudinal 

ill^/'>^s^  muscular 

layer. 


Outer  lon- 
gitudinal 
muscular 
layer. 


Fig.  297. — Cross-section  of  vas  deferens  near  the  epididymis  (human). 


numerous  folds,  which,  in  the  guinea-pig  for  instance,  present  a 
delicate  axial  connective -tissue  stroma.  Besides  scanty  subepithe- 
lial connective  tissue,  the  seminal  vesicles  are  provided  with  an  inner 
circular  and  an  outer  longitudinal  layer  of  muscle-fibers.  Sperma- 
tozoa are,  as  a  rule,  not  met  with  in  the  seminal  vesicles. 

The  epithelium  of  the  ejaculatory  ducts  is  composed  of  a  single 
layer  of  cells  ;  the  inner  circular  muscle-layer  is  very  poorly  devel- 
oped. In  the  prostatic  portion  of  the  ejaculatory  ducts  the  longi- 
tudinal muscle-layer  mingles  with  the  musculature  of  the  prostate 
and  loses  its  individuality.  The  ejaculatory  ducts  empty  either 
directly  into  the  urethra  at  the  colliculus  seminalis,  or  indirectly 
into  the  prostatic  portion  of  the  urethra  through  the  vesicula 
prostatica. 

The  prostate  is  a  compound  branched  tubulo-alyeolar  gland.      Its 


THE  MALE  GENITAL  ORGANS. 


369 


capsule  consists  of  dense  layers  of  nonstriated  muscle- fibers,  connec- 
tive tissue,  and  yellow  elastic  fibers.  Processes  and  lamellae  com- 
posed of  all  these  elements  extend  into  the  interior  of  the  gland,  con- 
verging toward  the  base  of  the  coUiculus  seminalis.  Between  the 
larger  trabeculae  are  situated  numerous  glands,  consisting  of  large. 


Fig.  298. — Cross-section  of  wall  of  seminal  vesicle,  showing  the  folds  of  the 
mucosa  (human). 


Fig.  299. — From  section  of  prostate  gland  of  man. 


irregular  alveoli,  separated  by  fibromuscular  septa  and  trabeculae. 
The  alveoli  are  lined  by  simple  columnar  epithelium,  the  inner 
portion  of  the  cells  often  showing  acidophile  granules.  Now  and 
then  the  alveoli  present  a  pseudostratified  epithelium,  with  two 
rows  of  nuclei  (Rudinger,  St,).      A  basement  membrane,  although 

24 


3/0  THE    GENITO-URINARY    ORGANS. 

present,  is  difficult  to  demonstrate  and  consists  of  a  network  of  deli- 
cate connective-tissue  threads,  as  was  shown  by  Walker.  The 
numerous  excretory  ducts,  lined  by  simple  columnar  epithelium,  be- 
come confluent  and  form  from  1 5  to  30  collecting  ducts  which  empty, 
as  a  rule,  either  at  the  coUiculus  seminalis  or  into  the  sulcus  prosta- 
ticus.  Near  their  terminations  the  larger  ducts  are  lined  by  transi- 
tional epithelium  similar  to  that  lining  the  prostatic  portion  of  the 
urethra. 

In  the  alveoli  of  the  glands,  peculiar  concentrically  laminated 
concrements  are  found,  known  as  prostatic  bodies  or  concretions 
(corpora  amylacea).  They  are  more  numerous  in  old  men,  but  are 
found  in  the  prostates  of  young  men  and  also  of  young  boys. 
The  secretion  of  the  prostate  (succus  prostaticus)  is  not  mucous 
in  character,  but  resembles  a  serous  secretion  and  has  an  acid  reac- 
tion. The  vesicula  prostatica  (sinus  pocularis)  is  lined  by  stratified 
epithelium,  consisting  of  two  layers  of  cells  and  provided  with  a  dis- 
tinct cuticular  margin  upon  which  rest  cilia.  In  its  urethral  region 
occur  short  alveolar  glands. 

The  glands  of  Cowper  are  branched  tubular  alveolar  glands,  the 
alveoli  being  lined  by  mucous  cells.  The  smaller  excretory  ducts, 
lined  by  cubical  epithelium,  unite  to  form  two  ducts,  one  on  each  side 
of  the  urethra  ;  these  are  i  i^  inches  long,  and  are  lined  by  strat- 
ified epithelium  consisting  of  two  or  three  layers  of  cells. 

The  blood-vessels  of  the  prostate  ramify  in  the  fibromuscular 
trabeculae  and  form  capillary  networks  surrounding  the  alveoli.  The 
veins  collecting  the  blood  pass  to  the  periphery  of  the  gland,  where 
they  form  a  plexus  in  the  capsule.  The  lymphatics  begin  in  clefts 
in  the  trabeculae  and  follow  the  veins.  The  terminal  branches  of 
the  vessels  supplying  Cowper's  glands  are,  in  their  arrangement, 
like  those  of  other  mucous  glands. 

Numerous  sympathetic  ganglia  are  found  in  the  prostate  under 
the  capsule  and  in  the  larger  trabeculae  near  the  capsule.  The 
neuraxes  of  the  sympathetic  cells  of  these  ganglia  may  be  traced 
to  the  vessels  and  into  the  trabeculae  ;  their  mode  of  ending  has, 
however,  not  been  determined.  Small  medullated  nerve-fibers 
terminate  in  these  ganglia  in  pericellular  baskets.  TimOfeew  has 
described  peculiar  encapsulated  sensory  nerve-endings,  found  in  the 
prostatic  and  membranous  portions  of  the  urethra  of  certain  mam- 
malia. They  consist  of  the  terminal  branches  of  two  kinds  of  nerves, 
inclosed  within  nucleated  laminated  capsules  :  one  large  medul- 
lated nerve -fiber,  after  losing  its  medullary  sheath,  breaks  up  into  a 
small  number  of  ribbon-shaped  branches  with  serrated  edges,  which 
may  pass  more  or  less  directly  to  the  end  of  the  nerve-ending  or 
may  be  bent  upon  themselves  ;  and  very  much  smaller  medullated 
nerve-fibers  which,  after  losing  their  medullary  sheaths,  divide  into- 
a  large  number  of  varicose  fibers  which  form  a  dense  network  en- 
circling the  ribbon-shaped  fibers  previously  mentioned. 

The  penis  consists  of  three  cylindric  masses  of  erectile  tissue 
— the  two  corpora  cavernosa,  forming  the  greater  part  of  the  penis 


THE  MALE   GENITAL    ORGANS.  3/1 

and  lying  side  by  side,  and  the  corpus  spongiosum,  surrounding 
the  urethra  and  lying  below  and  between  the  corpora  cavernosa. 
The  two  latter  are  surrounded  by  a  dense  connective-tissue  sheath, 
the  tunica  albuginea.  These  erectile  bodies  are  surrounded  by  a 
thin  layer  of  skin,  containing  no  adipose  tissue  and  no  hair-follicles. 
The  corpus  spongiosum  is  enlarged  anteriorly  to  form  the  glans 
penis. 

The  principal  substance  of  the  erectile  bodies  is  the  so-called 
erectile  tissue :  septa  and  trabeculae,  consisting  of  connective 
tissue,  elastic  fibers,  and  smooth  muscle-cells  inclosing  a  sys- 
tem of  communicating  spaces.  These  latter  may  be  regarded  as 
venous  sinuses,  the  walls  of  which,  lined  by  endothelial  cells,  are 
in  apposition  to  the  erectile  tissue.  Under  certain  conditions  the 
venous  sinuses  are  distended  with  blood,  but  normally  they  are  in 
a  collapsed  state  and  form  fissures  which  simulate  the  clefts  found 
in  ordinary  connective  tissue.  In  other  words,  there  is  here  such 
an  arrangement  of  the  blood-vessels  within  the  erectile  tissue  that 
the  circulation  may  be  carried  on  with  or  without  the  aid  of  the 
cavernous  spaces.  The  arteries  of  the  corpora  cavernosa  possess 
an  especially  well-developed  musculature.  They  ramify  through- 
out the  trabeculae  and  septa  of  the  erectile  tissue  and  break  up 
within  the  septa  into  a  coarsely  meshed  plexus  of  capillaries.  A  few 
of  these  arteries  empty  directly  into  the  cavernous  spaces.  On  the 
other  hand,  the  arteries  give  off  a  rich  and  narrow-meshed  capillary 
network  immediately  beneath  the  tunica  albuginea.  This  is  in  com- 
munication with  a  deeper  and  denser  venous  network,  which,  in  turn, 
gradually  empties  into  the  venous  sinuses.  Aside  from  these  there 
are  anastomoses  between  the  arterial  and  venous  capillaries,  which 
later  communicate  with  the  venous  network  just  mentioned.  The 
blood  current,  regulated  as  it  thus  is,  may  pass  either  through 
the  capillaries  alone,  or  may  divide  and  flow  through  both  these 
and  the  venous  sinuses.  These  conditions  explain  both  the  erec- 
tile and  quiescent  state  of  the  penis.  The  relations  are  somewhat 
different  in  the  corpus  spongiosum  urethrae  and  in  the  glans  penis. 
In  the  corpus  spongiosum  the  arteries  do  not  open  directly  into 
the  venous  spaces,  but  break  up  first  into  capillaries.  In  the  sub- 
mucosa  of  the  urethra  there  is  found  a  rich  venous  plexus.  In  the 
glands  the  arteries  end  in  capillaries  which  pass  over  into  veins  with 
well-developed  muscular  walls.  The  blood  is  collected  by  means 
of  the  venae  emissariae  which  empty  into  the  vena  dorsalis  penis  and 
into  the  venae  profundae. 

The  epithelium  of  the  urethra  varies  in  the  several  regions.  The 
prostatic  portion  possesses  an  epithelium  similar  to  that  of  the 
bladder.  In  the  membranous  portion,  the  epithelium  may  be  simi- 
lar to  that  found  in  the  prostatic  portion,  but  more  often  pre- 
sents the  appearance  of  a  pseudostratified  epithelium  with  two  or 
three  layers  of  nuclei.  The  cavernous  region  is  lined  by  pseudo- 
stratified epithelium,  except  in  the  fossa  navicularis,  where  a 
stratified  squamous  epithelium  is  found.      Between  the  fibro-elastic 


3/2  THE    GENITO-URINARY    ORGANS. 

mucosa  and  the  epithelium  there  is  a  basement  membrane.  There 
occur  in  the  urethra,  beginning  with  the  membranous  portion,  ir- 
regularly scattered  epithelial  sacculations  of  different  shapes.  Some 
of  these  show  alveolar  branching,  and  are  then  known  as  the  glands 
of  Littre. 

The  submucosa  of  the  cavernous  portion  of  the  urethra,  which 
contains  nonstriated  muscle-tissue  arranged  circularly,  is  richly  sup- 
plied with  veins,  and  contains  pronounced  plexuses  communicating 
with  cavernous  sinuses,  which  correspond  in  general  to  those  of  the 
corpora  cavernosa  penis. 

The  glans  is  covered  by  a  layer  of  stratified  squamous  epithe- 
lium, often  possessing  a  thin  stratum  corneum  (see  Skin).  Near 
the  corona  of  the  glans  penis  there  are  now  and  then  found  small 
sebaceous  glands  (see  Hair),  known  as  glands  of  Tyson.  The  pre- 
puce is  a  duplication  of  the  skin,  the  inner  surface  presenting  the 
appearance  of  a  mucous  membrane. 

The  nerves  terminating  in  the  glans  penis  have  recently  been 
studied  by  Dogiel,  who  made  use  of  the  methylene-blue  method  in 
his  investigation.  He  finds  Meissner's  corpuscles  in  the  connective- 
tissue  papillae  under  the  epithelium,  Krause's  spheric  end-bulbs 
somewhat  deeper  in  the  connective  tissue,  and  the  genital  corpuscles 
situated  still  deeper  (see  Sensory  Nerve-endings).  In  the  epithelium 
are  found  free  sensory  nerve-endings.  Pacinian  corpuscles  have 
also  been  found  in  this  region. 


4.  SPERMATOGENESIS. 

In  order  that  the  student  may  obtain  an  understanding  of  the  com- 
plicated process  of  spermatogenesis  we  shall  give  a  description  of  it 
as  it  occurs  in  salamandra  maculosa,  which  of  all  vertebrate  animals 
presents  the  phenomena  in  their  simplest  and  best  known  form. 
The  student  should  understand,  however,  that  many  of  the  details 
here  described  have  not  been  observed  in  the  testes  of  mammalia ; 
and,  since  the  spermatozoa  of  many  of  the  mammalia  are  of  simpler 
structure  than  those  of  the  salamander,  the  development  of  the 
spermatozoa  of  the  former  is  consequently  simpler.  It  should  also 
be  noticed  that  the  general  structure  of  the  testes  of  the  salamander 
differs  in  some  respects  from  that  of  the  testes  of  mammalia,  as  given 
in  the  preceding  pages. 

At  first  the  seminiferous  tubules  consist  of  solid  cellular  cords, 
and  it  is  only  during  active  production  of  spermatozoa  that  a  central 
lumen  is  formed,  in  which  the  spermatosomes  then  lie.  The  cells 
which  compose  these  solid  iords  may  be  early  differentiated  into  two 
classes — those  of  the  one  class  being  directly  concerned  in  the  pro- 
duction of  the  spermatosomes  ;  those  of  the  other  appearing  to  have 
a  more  passive  role.  The  cells  of  the  first  class — the  spermatogo- 
nia, or  primitive  seminal  cells — undergo  a  process  of  division  accom- 
panied by  an  increase  in  size.  In  this  way  they  soon  commence  to 
press  upon  the  cells  of  the  second  class — tho.  follicular  ov  siiste7itacu- 


SPERMATOGENESIS.  373 

lar  cells.  The  result  is  that  the  nuclei  of  the  latter  are  forced  more 
or  less  toward  the  wall  of  the  seminal  tubule,  while  their  proto- 
plasm is  so  indented  by  the  adjacent  spermatogonia  that  the  cells 
assume  a  flattened  cylindric  shape  presenting  indentations  and 
processes  on  all  sides.  In  this  stage  the  spermatogonia  have  a 
radiate  arrangement  and  entirely  surround  the  elongated  susten- 
tacular  cells.  At  present  three  periods  are  distinguished  in  the 
development  of  the  male  sexual  cells  (spermatosomes)  from  the 
spermatogonia.  The  first  period  embraces  a  repeated  mitotic  divi- 
sion of  the  spermatogonia — the  period  of  proliferation.  In  the  sec- 
ond, the  spermatogonia,  which  have  naturally  become  smaller  from 
repeated  division,  begin  to  increase  in  size — the  period  of  growth. 
The  third  is  characterized  by  a  modified  double  mitotic  division 
without  intervening  period  of  rest,  and  results  in  the  matured  sper- 
matozoa— the  period  of  maturation,  figure  300.  During  the  third 
period,  a  very  important  and  significant  process  takes  place — the 

Primordial  sexual  cell. 

• 


,  Zone  of  proliferation. 
Spermatogonia.,,  /       \  /        \  /  (The  generations  are 

'  ^  '         much  larger.) 


I"'"" 

Spermatocyte  I  order." 

Spermatocytes  II  order. "•  •  |  Zone  of  maturation. 

Spermatids. •        •        •      ^  ■——-.,.„  / 

Fig.  300. — Schematic  diagram  of  spermatogenesis  as  it  occurs  in  ascaris  (after  Boveri). 
("Ergebn.  d.  Anat.  u.  Entw.,"  Bd.  i.) 

reduction  in  the  number  of  chromosomes,  so  that  in  the  spermatids, 
the  chromosomes  are  reduced  to  half  the  number  present  in  a 
somatic  cell  of  the  same  animal.  The  manner  in  which  this  reduc- 
tion in  the  number  of  chromosomes  takes  place  will  be  described  as 
it  occurs  in  salamandra  maculosa. 

After  the  cells  composing  the  last  generation  of  spermato- 
gonia have  attained  a  certain  size  (period  of  growth),  they  under- 
go karyokinetic  division.  First,  the  usual  skein  or  spirem  is 
formed,  but  instead  of  dividing  into  twenty-four  chromosomes,  as 
in  the  somatic  cell,  the  filament  of  the  skein  segments  into  only 
twelve  loops.  The  cell  thus  provided  with  twelv^e  chromosomes 
now  enters   upon   the   period  of   maturation,    and   is  known   as  a 


374  THE    GENITO-URINARY    ORGANS. 

spermatocyte  of  the  first  order,  or  a  "mother  cell"  (O.  Hert- 
wig,  90).  The  division  of  these  cells  is  heterotypic  {vid.  p.  70); 
the  chromosomes  split  longitudinally  and  in  such  a  way  that  the 
division  begins  at  the  crown  of  the  loops,  extending  gradually 
toward  their  free  ends.  In  this  case  the  daughter  chromosomes 
remain  for  some  time  in  contact,  so  that  the  metakinetic  figure 
resembles  a  barrel  in  shape.  Finally,  the  daughter  chromosomes 
separate  and  wander  toward  the  poles.  As  soon  as  the  daughter 
stars  (diaster)  are  developed,  the  number  of  chromosomes  is  again 
doubled  by  a  process  of  longitudinal  division.  The  spermatocyte 
of  the  first  order  thus  divides  into  two  spermatocytes  of  the  second 
order,  or  daughter  cells  (O.  Hertwig,  90).  The  nuclei  of  the 
daughter  cells  now  contain  twenty-four  chromosomes,  as  is  the 
case  in  the  somatic  cell,  and,  without  undergoing  longitudinal  split- 
ting, the  daughter  chromosomes  are  distributed  to  the  two  nuclei 
of  the  spermatids.  In  other  words,  the  latter  contain  only  twelve 
chromosomes.  The  spermatozoa  are  formed  from  the  spermatids 
by  a  rearrangement  of  the  constituent  elements  of  these  cells.  It 
may  thus  be  said  that  even  in  the  stage  of  the  segmenting  skein  in 
the  mother  cells,  the  spermatocytes  of  the  first  degree  contain  twice 
as  many  chromosomes  as  a  somatic  cell,  a  condition  which  is 
first  clearly  seen  in  the  stage  of  the  diaster  (here  only  an  apparent 
duplication  in  the  diaster  stage).  As  a  result,  there  is,  first,  a  de- 
crease in  the  double  number  of  chromosomes  found  in  the  sperma- 
tocytes of -the  second  degree  to  the  normal  number;  second,  a 
decrease  in  the  number  of  chromosomes  in  the  spermatocytes  of  the 
third  degree  (spermatids)  to  one-half  the  number  present  in  a 
somatic  cell,  a  condition  probably  due  to  the  fact  that  here  there 
is  no  stage  of  rest  nor  longitudinal  splitting  of  the  chromosomes. 
This  is  the  general  process  in  heterotypic  division.  Besides  the 
heterotypic  form,  there  occurs  in  the  division  of  the  spermatocytes 
another  (homeotypic)  form  of  karyokinetic  cell-division.  This  dif- 
fers from  the  heterotypic  in  the  shortness  of  the  chromosomes,  the 
absence  of  the  barrel  phase,  the  late  disappearance  of  the  aster, 
and  the  absence  of  duplication  in  the  chromosomes  of  the  diaster. 
According  to  Meves  (96),  the  spermatocytes  of  the  first  degree 
undergo  heterotypic,  those  of  the  second  degree,  homeotypic 
division. 

The  spermatids  develop  into  the  spermatozoa,  beginning  imme- 
diately after  the  close  of  the  second  division  of  maturation.  This 
process  has  been  fully  described  for  salamandra  maculosa  by  Her- 
mann, Flamming,  Benda,  and  others,  but  need  not  engage  our 
attention  at  this  point  beyond  the  statement  that  the  chromatin  of 
the  nuclei  of  the  spermatids  develops  into  the  heads  of  the  sperma- 
tozoa, while  the  remaining  structures  are  developed  from  the  proto- 
plasm. "  The  mature  spermatozoon  of  the  salamander  represents 
a  completely  metamorphosed  rell ;  in  the  course  of  its  develop- 
ment no  portion  of  the  original  cell  is  cast  off"  (Meves,  97). 

Spermatogenesis  in  mammalia  may  be  compared  to  the  foregoing 


SPERMATOGENESIS. 


375 


process,  with  the  exception  that  here  the  different  stages  are  seen 
side  by  side  in  the  seminiferous  tubule  and  without  any  apparent 
sequence,  making  the  successive  stages  more  difficult  to  demon- 
strate. The  various  generations  of  cells  form  columns,  and  are 
arranged  in  such  a  manner  that  the  younger  are  found  near  the 
lumen  and  the  older  close  to  the  wall  of  the  tubule.   (Figs.  301  and 


Fig.  301  • — Schematic  diagram  of  section  through  convoluted  seminiferous  tubule 
of  mammal,  showing  the  development  of  the  spermatosomes.  The  number  of  chromo- 
somes is  not  shown  in  the  various  generations  of  the  spermatogenic  cells.  The  pro- 
gressive development  of  the  spermatogenic  elements  is  illustrated  in  the  eight  sectors 
of  the  circle  :  a.  Young  sustentacular  cell ;  b,  spermatogonium  ;  c,  spermatocyte  ;  d, 
spermatid.  In  i,  2,  3,  and  4  the  spermatids  rest  on  the  enlarged  sustentacular  cell  in  the 
center  of  the  sector  ;  on  both  sides  of  the  sustentacular  cells  are  the  spermatogenic  or 
mother  cells  in  mitosis.  In  the  sectors  5,  6,  7,  and  8  spermatozoa  are  seen  in  ad- 
vanced stages  resting  on  the  sustentacular  cells,  with  new  generations  of  spermatids  on 
each  side.      [From  Rauber  (after  Brown)  with  changes  (after  Hermann).] 


302.)  These  columns  are  separated  from  each  other  by  high  sus- 
tentacular cells,  or  Sertoli's  cells  or  columns.  The  metamorphosis 
of  the  cells  into  spermatids  and  spermatosomes  is  accomplished 
by  the  changing  of  the  cells  bordering  upon  the  lumen  and  then 
of  those  in  the  deeper  layers,  etc.,  into  spermatids  and  then 
into  spermatosomes.      During  this  process  the  spermatids  arrange 


3/6  THE    GENITO-URINARY    ORGANS. 

themselves  around  the  ends  of  SertoH's  columns,  a  phenomenon 
which  was  formerly  regarded  as  representing  a  copulation  of  the 
two  elements,  although  it  was  clearly  understood  that  no  real 
fusion  or  interchange  of  chromatin  occurred,  but  that  the  close 
relations  of  the  two  were  for  the  purpose  of  furnishing  nourishment 
to  the  developing  spermatosomes.  The  whole  forms  a  spermato- 
blast of  von  Ebner.  Since  the  spermatids  lining  the  lumen  are 
changed  into  spermatozoa,  and  the  process  is  repeated  in  the  cells 
of  the  deeper  layers  as  they  come  to  the  surface,  the  result  is  that 
the  entire  column  is  finally  used  up.  The  compensatory  elements 
are  supplied  by  the  proliferation  of  the  adjacent  spermatogonia. 
The  resulting  products  again  divide,  and  thus  build  up  an  entirely 
new  generation  of  spermatogenic  cells.  Hand  in  hand  with  these 
progressive  phenomena  occurs  an  extensive  destruction  of  the  cells 
taking  part  in  spermatogenesis.  This  is  shown  by  the  presence  of 
so-called  karyolytic  figures  in  the  cells,  which  later  suffer  complete 
demolition. 

These  developmental   changes   are  represented  in  the  preced- 


Fig.  302. — Section  of  convoluted  tubule  from  rat's  testicle  (after  von  Ebner, 
88).  The  pyramidal  structures  are  the  sustentacular  cells,  together  with  spermatids  and 
spermatosomes.  Between  these  are  spermatogenic  cells,  some  of  which  are  in  process 
of  mitotic  division.  Below,  on  the  basement  membrane  and  concealing  the  spermato- 
gonia, are  black  points  representing  fat-globules,  a  characteristic  of  the  rat's  testicle. 
Fixation  with  Flemming's  fluid. 

ing  schematic  figure  (Fig.  301),  and  may  in  part  be  observed  in 
figure  302. 

In  mammalia  it  has  been  possible  to  trace  the  development 
of  the  spermatids  into  the  spermatosomes.  These  phenomena  have 
been  studied  and  described  by  numerous  writers,  and  although 
many  conflicting  views  have  been  expressed,  the  essential  steps  of 
this  process  seem  quite  clearly  established.  The  account  here 
given  is  based  in  part  on  the  recent  observations  of  v.  Lenhossek 
and  the  observations  of  Benda.  Before  considering  the  method  of 
development  of  the  spermatosomes  from  the  spermatids,  a  few  words 
concerning  the  structure  of  the  latter  may  be  useful.  The  sharply 
outlined  spermatid  possesses  a  slightly  granular  protoplasm  and  a 
round  or  slightly  oval  nucleus  with  a  delicate  chromatic  network. 
In  the  protoplasm  there  is  found  a  sharply  defined  globule,  known 
as  the  sphere  or  sphere  substance,  which  lies  near  the  nucleus  and 


SPERMATOGENESIS.  377 

presents  throughout  a  nearly  homogeneous  structure.  This  sub- 
stance is  first  noticed  in  the  spermatocytes,  disappears  during  the 
cell-divisions  resulting  in  the  spermatids,  and  reappears  in  the  latter. 
In  the  protoplasm  of  the  spermatid,  lying  near  the  nucleus,  there 
is  further  found  a  small  globular  body,  the  chromatoid  accessory 
nucleus  of  Benda,  smaller  than  the  sphere  and  staining  very  deeply 
in  Heidenhain's  hematoxylin.  A  true  centrosome  may  also  be 
found  in  the  spermatid. 

The  nucleus  of  the  spermatid  develops  into  the  head  of  the 
spermatosome,  during  which  change  the  originally  spheric  nucleus 
becomes  somewhat  flattened  and  at  the  same  time  assumes  a  denser 
structure  and  moves  toward  that  portion  of  the  spermatid  pointing 
away  from  the  lumen  of  the  seminiferous  tubule.  Accompanying 
these  changes  in  the  nucleus,  marked  changes  are  observed  in  the 
shape  and  structure  of  the  sphere,  which  marks  the  position  of  the 
future  anterior  end  of  the  head  of  the  spermatosome,  and  applies 
itself  to  the  nucleus  on  the  side  pointing  away  from  the  lumen  of 
the  tubule.  In  this  position  it  differentiates  into  an  outer  clear 
homogeneous  zone  and  a  central  portion  which  stains  more  deeply 
and  to  which  v.  Lenhossek  has  given  the  name  akrosome.  From 
these  structures  are  developed  the  head-cap  and  the  lance  of  the 
spermatosomes,  which  differ  in  shape  and  relative  size  in  the  sper- 
matosomes  of  the  different  vertebrates.  Recent  investigation  seems 
to  establish  quite  clearly  that  the  axial  thread  of  the  tail  is  devel- 
oped from  the  centrosome  (from  the  larger,  if  two  are  present),  which 
is  situated  at  some  distance  from  the  nucleus.  Soon  after  the  begin- 
ning of  the  development  of  the  axial  thread  the  centrosome  wanders 
to  the  posterior  part  of  the  future  head  of  the  spermatosome  (the 
pole  of  the  nucleus  opposite  the  head-cap)  and  becomes  firmly 
attached  to  the  nuclear  membrane  in  this  position  (observations 
made  on  the  rat  by  v.  Lenhossek,  and  on  the  salamander  by  Meves). 
The  middle  piece  and  the  undulating  membrane,  it  would  appear, 
are  differentiated  from  the  protoplasm,  although  the  question  of  the 
mode  of  their  development  is  still  open  to  discussion.  The  chro- 
matoid body  assumes  a  position  near  the  axial  thread  at  its  junc- 
tion with  the  cell  membrane ;  its  fate  has  not,  however,  been  fully 
determined. 

According  to  Hermann  (97),  the  end-piece  in  the  selachia  is 
derived  from  the  centrosome,  the  ring-shaped  body  from  the  invagi- 
nated  half  of  the  intermediate  body  of  the  spermatid  formed  during 
the  last  spermatocytic  division,  and  the  axial  thread  from  filaments  of 
the  proximal  half  of  the  central  spindle.  The  lance,  according  to 
him,  represents  a  modified  portion  of  the  nuclear  membrane  of  the 
spermatid. 

For  further  particulars  regarding  spermatogenesis  see  the  in- 
vestigations of  V.  la  Valette  St.  George,  67-87  ;  v.  Brunn,  84 ; 
Biondi,  Benda,  Meves,  and  v.  Lenhossek. 


378 


THE    GENITO-URINARY    ORGANS. 


TECHNIC. 


The  ovaries  of  the  smaller  animals  are  better  adapted  to  study 
than  those  of  the  human  being,  since  the  former  are  more  easily  fixed. 

The  germinal  epithelium  and  its  relations  to  the  egg-tubes  of 
Pflüger  are  best  studied  in  the  ovaries  of  young  or  newly  born  animals — 
cats,  for  instance,  being  especially  well  adapted  to  this  purpose. 

Normal  human  ovaries  are  usually  not  easily  obtainable.  Human 
ovaries  very  often  show  pathologic  changes,  and  in  middle  life  frequently 
contain  but  few  follicles. 

Fresh  ova  may  be  easily  procured  from  the  ovaries  of  sheep,  pig, 
or  cow  in  the  slaughter-houses.  On  their  surfaces  are  prominent  trans- 
parent areas — the  larger  follicles.  If  a  needle  be  inserted  into  one  of 
these  follicles  and  the  liquor  folliculi  be  caught  upon  a  slide,  the  ovum 
may  as  a  rule  be  found,  together  with  its  corona  radiata.  That  part  of 
the  preparation  containing  the  ovum  should  be  covered  with  a  cover-glass 
under  the  edges  of  which  strips  of  cardboard  are  laid.  If  no  such  strips 
are  employed,  the  zona  pellucida  of  the  ovum  is  likely  to  burst  in  the  field 
of  vision,  giving  rise  to  a  funnel-shaped  tear.  These  tears  have  often 
been  pictured  and  described  as  preformed  canals  (micropyles) . 

The  best  fixing  fluid  for  ovarian  tissue  is  Flemming's  or  Her- 
mann's, either  of  which  may  be  used  for  small  ovaries  or  pieces  of  large 
ovaries  ;  safranin  is  then  used  for  staining.  Good  results  are  also  ob- 
tained with  corrosive  sublimate  (staining  with  hematoxylin  according 
to  M.  Heidenhain),  and  also  with  picric  acid  (staining  with  borax- 
carmin). 

The  treatment  of  the  Fallopian  tubes  is  the  same  as  that  of  the 
intestine  ;  in  order  to  obtain  cross-sections  of  a  tube  it  is  advisable  to  dis- 
sect away  the  peritoneum  near  its  line  of  attachment  and  then  distend  the 
tube  before  fixing.  It  is  instructive  to  dilate  the  tube  by  filling  it  with 
the  fixing  agent,  thus  causing  many  of  the  folds  to  disappear. 

No  special  technic  is  necessary  in  fixing  the  uterus  and  vagina. 
The  epithelium  is,  however,  best  isolated  with  one-third  alcohol. 

Seminal  fluid  to  which  normal  salt  solution  has  been  added  may 
be  examined  in  a  fresh  condition.  The  effect  upon  the  spermatozoa  of  a 
very  dilute  solution  of  potassium  hydrate  ( i  ^  or  weaker)  or  of  a  very 
dilute  acid  (acetic  acid)  is  worth  noticing.  The  spermatozoa  of  sala- 
mandra  maculosa  show  the  different  structural  parts  very  clearly  (lance, 
undulating  membrane,  marginal  thread,  etc.).  In  macerated  prepara- 
tions (very  dilute  chromic  acid),  or  in  those  left  for  some  time  in  a 
moist  chamber,  the  fibrillar  structure  of  the  marginal  and  axial  threads 
may  be  seen  quite  distinctly.  The  spermatozoa  may  also  be  examined 
in  the  form  of  dry  preparations  (treatment  as  for  blood),  stained,  for 
instance,  with  safranin.  Osmic  acid,  its  niixtures,  and  osmic  vapors  are 
useful  as  fixing  agents,  certain  structures  being  better  brought  out  so  than 
by  employing  the  dry  methods. 

In  examining  the  testicle  (spermatogenesis)  it  is  advisable  to 
begin  with  the  testis  of  the  salamander,  which  does  not  show  such  com- 
plicated structures  as  do  the  testes  of  mammalia.  Here  also  either  Flem- 
ming's or  Hermann's  fluid  may  be  used  as  a  fixing  agent,  the  latter  being 


THE    SKIN.  379 

followed  by  treatment  with  crude  pyroligneous  acid.  For  the  salaman- 
der Hermann  recommends  a  mixture  composed  of  i  ^  platinum  chlorid 
15  c.c,  2^  osmic  acid  2  c.c,  and  glacial  acetic  acid  i  c.c,  and  for 
mammalia  the  same  solution  with  double  the  amount  of  osmic  acid. 
The  fluid  is  allowed  to  act  for  some  days,  the  specimen  then  being 
washed  for  twenty-four  hours  in  running  water  and  carried  over  into  alco- 
hols of  ascending  strengths.  Paraffin  sections  are  treated  as  follows  : 
Place  for  from  twenty-four  to  forty-eight  hours  in  safranin  (safranin  i 
gm.  is  dissolved  in  10  c.c.  of  absolute  alcohol  and  diluted  with  90  c.c. 
of  anilin  water).  After  decolorizing  with  pure  or  acidulated  absolute 
alcohol  the  sections  are  placed  for  three  or  four  hours  in  gentian -violet 
(saturated  alcoholic  solution  of  gentian -violet  5  c.c.  and  anilin  water 
100  c.c),  and  are  then  placed  for  a  few  hours  in  iodo-iodid  of  potassium 
solution  until  they  have  become  entirely  black  (iodin  i,  iodid  of  potas- 
sium 2,  water  300);  finally,  they  are  washed  in  absolute  alcohol,  until 
they  become  violet  with  a  dash  of  brown.  The  various  structures  appear 
differently  stained  :  for  instance,  the  chromatin  of  the  resting  nucleus 
and  of  the  dispirem,  bluish -violet ;  the  true  nucleoli,  red  ;  while,  on  the 
other  hand,  in  the  aster  and  diaster  stages  the  chromatin  stains  red. 

It  is  of  especial  importance  that  small  testicles  should  not  be  cut  into 
pieces  before  fixing,  as  this  causes  the  seminal  tubules  to  swell  up  and 
show  marked  changes,  even  in  regions  at  some  distance  from  the  cut 
(Hermann,  93,  I). 

The  treatment  of  the  remaining  parts  of  the  male  reproductive  organs 
requires  no  special  technic. 


VI.  THE  SKIN  AND  ITS  APPENDAGES. 

A.  THE  SKIN  (CUTIS). 

The  skin  consists  of  two  intimately  connected  structures — the 
one,  of  mesodermic  origin,  is  the  true  skin,  corium  or  dermis ;  the 
other,  of  ectodermic  origin,  is  the  epidermis  or  cuticle.  The  super- 
ficial layer  of  the  corium  is  raised  into  ridges  and  papillae  which 
penetrate  into  the  epidermis,  the  spaces  between  the  papillae  being 
filled  with  epidermal  elements.  Thus,  the  lower  surface  of  the 
epidermis  is  alternately  indented  and  raised  into  a  system,  of  furrows 
and  elevations  corresponding  to  the  molding  of  the  corium. 

In  the  epidermis  two  layers  of  cells  may  be  observed — the 
stratum  Malpighii,  or  stratum  germinativum  (Flemming),  and  the 
horny  layer,  or  stratum  corneum.  According  to  the  shape  and 
characteristics  of  its  cells,  the  stratum  germinativum  may  also  be 
divided  into  three  layers — first,  the  deep  or  basal  layer,  consisting 
of  columnar  cells  resting  immediately  upon  the  corium  ;  second, 
the  middle  layer,  consisting  of  polygonal  cells  arranged  in  several 
strata,  the  number  of  the  latter  varying  according  to  the  region  of 
the  body ;  and  third,  the  upper  layer,  or  stratum  granidosiim, 
which  is  composed,  at  most,  of  two  or  three  strata  of  gradually 
flattening  cells   characterized  by  their  peculiar  granular  contents. 


38o 


THE   SKIN   AND    ITS    APPENDAGES. 


All  these  cell  layers  consist  of  prickle  cells,  and  for  this  reason  the 
stratum  Malpighii  is  sometimes  known  as  the  stratum  spinosum. 
When  these  cells  are  isolated  by  certain  methods,  their  surfaces  are 
seen  to  be  provided  with  short,  thread-like  processes.  In  section 
the  cells  appear  to  be  joined  together  by  their  processes.  Since  it 
has  been  proved  that  the  processes  of  adjacent  cells  do  not  lie  side 
by  side,  but  meet  and  fuse,  they  must  be  regarded  as  belonging  alike 
to  both  cells.  Between  the  fused  processes,  which  are  known  as 
intercellular  bridges,  there  exists  a  system  of  channels  which  is  in 
communication  with  the  lymphatic  system  of  the  corium.  The 
prickles  just  mentioned  are  variously  regarded  by  different  investi- 
gators ;    some    considering  them  to  be   exclusively  protoplasmic 


Fig.  303. — Under  surface  of  the  epidermis,  separated  from  the  cutis  by  boiUng.  The 
sweat-glands  may  be  traced  for  a  considerable  part  of  their  length ;  X  4°  •'  ^>  Sweat- 
gland  ;  b,  longitudinal  ridge  ;  c,  depression ;  d,  cross-ridge. 

processes  of  the  cells,  others  regarding  them  as  derived  from  the 
membranes  of  the  cells  composing  the  stratum  Malpighii.  Ranvier 
and  others  ascribe  a  fibrillar  structure  to  the  peripheral  portion  of 
the  cellular  protoplasm,  and,  according  to  them,  these  fibrillse, 
surrounded  by  a  small  quantity  of  indifferent  protoplasm,  form 
the  processes.  Ranvier  has  also  shown  that  such  fibrillae  may 
extend  from  one  cell  around  several  others  befoi-e  reaching  their 
ultimate  destination  in  other  cells  at  some  distance.  (Fig.  305.)  The 
cells  of  the  stratum  granulosum  contain  peculiar  deposits  of  a  sub- 
stance to  which  Waldeyer  has  given  the  name  of  keratohyalin. 
This  substance  occurs  in  the  form  of  irregular  bodies  varying  in  size 
and  imbedded  in  the  protoplasm.      The  nuclei  of  such  cells  always 


THE    SKIN. 


381 


show  degenerative  processes,  which  are  possibly  due  to  the  forma- 
tion of  the  keratohyahn  (Mertsching,  Tettenhamer).  These  karyo- 
lytic  figures  and  keratohyalin  possess  in  common  many  apparently 
identical  microchemic  peculiarities,  and  it  is  very  probable  that 
karyolysis  and  the  formation  of  keratohyalin  are  processes  origin- 
ally very  closely  allied-^?,  e.,  that  the  keratohyalin  is  derived  from 
the  fragments  of  the  dying  nucleus. 

The  stratum  corneum  forms  the  outer  layer  of  the  epidermis  and 
presents,  as  a  rule,  a  somewhat  differentiated  lower  stratum.     This 


Duct  of  sweat-- - 
gland. 

Corium. 


Subcutis. . 


Stratum  corneum. 


</'■;•  ]'i/)f''y-c'  Stratum  Malpighii. 


Blood-vessel. 

^  -  -Sweat-gland.  ] 


Fig.  304. — Cross-section  of  skin  of  child,  with  blood-vessels  injected  ;  X  Sp- 
latter is  more  especially  noticeable  in  those  regions  in  which  the 
stratum  corneum  is  highly  developed,  and  is  known  as  the  stratum 
lucidum.  It  is  quite  transparent,  this  property  being  due  to  the 
presence  in  its  cells  of  a  homogeneous  substance,  which  is  in 
all  probability  a  derivative  of  the  more  solid  keratohyalin  of 
the  stratum  granulosum.  The  cells  of  the  stratum  corneum  are 
more  or  less  flattened  and  cornified,  especially  at  their  periphery. 
This  applies  more  particularly  to  the  superficial  cells.  In  the  inte- 
rior of  each  cell  a  more  or  less  degenerated  nucleus  may  be  seen, 
but  otherwise  its  contents  are  homogeneous,  or,  at  most,  arranged 


2,^2 


THE    SKIN   AND    ITS    APPENDAGES. 


in  concentric  lamellae  (Kölliker,  89).  Here  and  there  between  the 
cornified  cells  structures  may  be  seen  which  probably  represent  the 
remains  of  intercellular  bridges.  The  thickness  of  the  epidermis 
varies  greatly  according  to  the  locality,  and  is  directly  proportionate 
to  the  number  of  its  cell  layers.  As  a  rule,  the  stratum  Malpighii 
is  thicker  than  the  stratum  corneum,  but  in  the  palm  of  the  hand 
and  the  sole  of  the  foot  the  latter  is  considerably  the  thicker. 

The  various  layers  of  the  epidermis  are  in  close  genetic  relation- 
ship to  one  another.  The  constant  loss  to  which  the  epidermis  is 
subjected  by  desquamation  is  compensated  by  a  continuous  upward 
pushing  of  its  lower  elements  ;  cell-proliferation  occurs  in  the 
basal  cells  and  adjacent  cellular  strata  of  the  stratum  germinativum 
(Malpighii),  where  the  elements  are  often  seen  in  process  of  mitotic 
division.  The  young  cells  are  gradually  pushed  outward,  and  dur- 
ing their  course  assume  the  general  characteristics  of  the  elements 

composing  the  layers 
through  which  theypass. 
For  instance,  such  a  cell 
changes  first  into  a  cell 
of  the  stratum  germina- 
tivum ;  then,  when  it 
commences  the  forma- 
tion of  keratohyalin,  into 
a  cell  of  the  stratum 
granulös  um  ;  later,  into 
a  cell  of  the  stratum  lu- 
cidum, and  finally  into 
an  element  of  the  stra- 
tum corneum,  where  it 
loses  its  nucleus,  corni- 
fies,  and  at  last  drops  off. 
The  mesodermic  por- 
tion of  the  skin,  the  co- 
riiim,  consists  of  a  loose, 
subcutaneous  connective  tissue  containing  fat,  the  subcutaneous 
layer,  with  the  panniculus  adiposus,  and  of  the  true  skin,  or 
corium  proper.  The  amount  of  adipose  tissue  in  the  subcutaneous 
layer  is  subject  to  great  variation  ;  there  are,  however,  a  few  re- 
gions in  which  there  is  normally  very  little  or  no  fat  (external  ear, 
eyelids,  scrotum,  etc.).  To  the  subcutaneous  connective  tissue  is 
due  the  mobility  of  the  skin.  The  corium  may  be  compared  to  the 
mucosa  of  a  mucous  membrane,  and  consists  of  two  layers — of  a 
deeper  and  looser /«ri"  reticularis,  and  of  a  su'pQv^cidil  pars  papillaris 
supporting  the  papillae.  The  transition  from  the  one  to  the  other 
is  very  gradual.  Elastic  fibers  are  present  in  the  connective  tissue 
of  both  layers. 

The  pars  reticularis  is  made  of  bundles  of  connective-tissue  fibers 
arranged  in  a  network,  nearly  all  of  the  strands  of  which  have  a  direc- 


Fibrils  which 
pass  from  one 
cell  to  another. 

Nucleolus. 


Intercellular 
bridges. 


Nucleus  of 
cell. 


Fig.  305. 


-Prickle  cells  from  the  stratum  Malpighii 
of  man  ;  X  4^0' 


THE    SKIN, 


383 


tion  parallel  with  the  surface  of  the  skin  and  are  surrounded  by  a  retic- 
ulum of  rather  coarse  elastic  fibers.  In  that  portion  of  the  pars  papil- 
laris bordering  upon  the  epidermis,  the  interlacing  strands  of  con- 
nective tissue,  as  well  as  the  surrounding  reticulum  of  elastic  fibers, 
are  finer,  so  that  the  whole  tissue  is  denser.  This  stratum  supports 
the  papillje — knob-like  or  conical  elevations  of  still  denser  tissue  end- 
ing in  one  or  more  points.  We  accordingly  speak  of  simple  or  com- 
pound papillae.  These  structures  are  especially  numerous  and  well 
developed  in  the  palm  of  the  hand  and  sole  of  the  foot,  where  they 
are  from  1 10  //  to  220  //  long.  Here  they  rest  upon  ridges  of  the 
corium,  which  are  nearly  always  arranged  in  double  rows.  Accord- 
ing to  whether  the  papillae  contain  blood-vessels  alone,  or  special 
nerve-endings  also,  they  are  known  as  vascular  or  tactile  papillae. 


Lower  border 
of    stratum 
lucidum. 
Stratum  granu- 
losum. 


Fig.  306.— Cross-section  of  human  epidermis  ;  the  deeper  layers  of  the  stratum 
Malpighii  are  not  represented  ;  X  75°- 


The  smallest  papillae  are  found  in  the  mammae  and  scrotum — from 
30  //  to  50  //  long.  The  surface  of  the  pars  papillaris  is  covered  by 
an  extremely  delicate  membrane — the  basement  membrane.  Accord- 
ing to  most  authors,  the  basal  cells  of  the  epidermis  are  simply 
cemented  to  this  structure.  Others  believe  that  the  epithelial  cells 
are  provided  with  short  basilar  processes  which  penetrate  into  the 
basement  membrane  and  meet  here  with  similar  structures  from  the 
connective-tissue  cells  of  the  corium.  This  would  give  the  base- 
ment membrane  a  fibrillar  structure  (Schuberg). 

The  subcutaneous  layer  contains  numerous  more  or  less  verti- 
cal strands  of  connective  tissue,  containing  numerous  large  elastic- 
tissue  fibers  and  joining  the  stratum  reticulare  of  the  corium  to  the 


384 


THE   SKIN  AND    ITS    APPENDAGES. 


superficial  fascia  of  the  body  or  underlying  structure,  whatever  that 
may  be.  These  strands  are  the  retinaculce  cutis,  and  inclose  in 
their  meshes  masses  of  fatty  tissue  which  form  the  panniculus 
adiposiis.  The  latter  varies  greatly  in  thickness  in  different  parts 
of  the  body.  The  vertically  arranged  cords  of  connective  tissue 
are  accompanied  by  blood-vessels,  nerves,  and  the  excretory  ducts 
of  glands. 

Smooth  muscle-fibers  are  also  present  in  the  skin,  and  around 
the  hair  follicles  are  grouped  into  bundles.  Nearly  continuous 
layers  of  smooth  muscle  tissue  are  found  in  the  subcutaneous  layer 
of  the  scrotum  (forming  here  the  tunica  dartos),  in  the  perineum, 
in  the  areolae  of  the  mammae,  etc.  In  the  face  and  neck  striated 
muscle-fibers  also  extend  outward  into  the  corium. 

Even  in  the  white  race  certain  regions  of  the  epidermis  always 
contain  pigment — as,  for  instance,  the  areolae  and  mammillae  of  the 


Process  of ^ 

pigment  ~~ 

cell. 


^% ''"'■%  '  ^^^:/?^Ä'' 


Stratum 
corneum. 


Pigment 
-     cell    with 
two     pro- 
cesses! 

Pigmented 
basal  cell. 


{■' 


Fig.  307. — Cross-section  of  negro's  skin,  showing  the  intimate  relationship  of  the 
pigment  cells  of  the  corium  to  the  basilar  cells  of  the  epidermis.  The  latter  are  more 
deeply  pigmented  at  their  outer  ends.  The  pigment  granules  may  be  traced  into  the 
outermost  layers  of  the  stratum  corneum  ;  X  525. 


mammary  glands,  the  scrotum,  labia  majora,  around  the  anus,  etc. 
In  these  regions  the  epithelial  cells  and  the  connective-tissue  cells  of 
the  pars  papillaris  corii  contain  a  variable  number  of  small  pigment 
granules.  The  latter  occur  chiefly  in  the  basal  cells  of  the  epider- 
mis and  diminish  perceptibly  in  the  cells  of  the  overlying  layers,  so 
that  in  those  of  the  stratum  corneum  few,  if  any,  are  left.  In 
negroes  and  other  colored  races  the  deep  pigmentation  is  due  to  a 
similar  distribution  of  the  pigment  granules  in  the  entire  epidermis ; 
but  even  here  the  pigmentation  decreases  toward  the  surface, 
although  the  uppermost  cells  of  the  stratum  corneum  always  con- 
tain some  pigment.  The  nuclei  of  the  cells  are  always  free  from  the 
coloring-matter.  The  question  as  to  the  origin  of  the  pigment  is 
as  yet  unsolved.  This  much  is  known  :  that  in  those  regions  where 
pigment  is  present  certain  branched  and  deeply  pigmented  connec- 


THE    SKIN. 


385 


tive-tissue  cells  are  found  immediately  beneath  the  epidenrj's,  sending 
out  processes  which  may  be  traced  outward  between  the  cells  of 
the  stratum  Malpighii  (Aeby).  This  fact  has  led  some  authors  to 
believe  that  the  connective  tissue  is  in  reality  the  source  of  the  pig- 
ment, and  that  by  some  unknown  process  the  latter  is  taken  up  and 
conveyed  to  the  cells  of  the  epidermis.  This  theory  would  preclude 
a  direct  production  of  pigment  granules  in  the  epidermal  cells.  But 
although  it  can  not  be  denied  that  the  pigment  may  be  derived  from' 
the  connective  tissue,  it  is  hardly  logical  to  assume  a  priori  that 
epithelial  cells  are  not  capable  of  pigment  production,  since,  in  other 
regions  of  the  body,  pigment  formation  may  be  observed  in  cells  of 
undoubted  epithelial  origin,  as,  for  instance,  in  ganglion  cells  and  in 


Fig.  308. — A  reconstruction  showing  the  arrangement  of  the  blood-vessels  in  the 
skin  of  the  sole  of  the  foot  (Spalteholz):  a.  Stratum  Malpighii  and  corium ;  l>,  boundary 
between  cutis  and  subcutis,  in  the  region  of  the  coiled  portions  of  the  sweat-glands ; 
c,  subcutis;  d,  subpapillary  arterial  network  ;  e,  cutaneous  arterial  network;  f,  g,  h,  and. 
/',  first,  second,  third,  and  fourth  venous  plexuses. 


the  pigment  epithelium  of  the  retina.  An  interesting  proof  that  the 
processes  of  pigmented  connective -tissue  cells  actually  penetrate  the 
epidermis  is  afforded  by  the  case  reported  by  Karg,  of  transplanta- 
tion of  a  piece  of  skin  from  a  white  man  to  a  negro.  After  some 
time  the  piece  of  white  skin  became  pigmented.  Reinkehas  demon- 
strated that  the  pigment  in  certain  cells  is  in  combination  with 
certain  definite  bodies.  The  latter  have  been  given  the  botanical 
name  of  trophoplasts.  If  the  pigment  be  removed,  colorless  tropho- 
plasts  are  left.  They  may  be  tinged  with  certain  stains.  In  the 
epidermis  of  the  white  race  trophoplasts  are  also  constanth'  present, 
although  they  are  only  slightly  or  not  at  all  pigmented  (Barlow). 
25 


386 


THE    SKIN    AND    ITS    APPENDAGES. 


Stratum 
corneum. 


The  following  may  be  said  concerning  the  vascular  system  of  the 
skin  :  The  arteries  which  supply  the  skin  with  nutriment  penetrate 
the  corium  and  form  a  characteristic  network  in  its  lowest  stratum. 
They  also  anastomose  freely  in  the  fascia  and  the  subcutaneous 
layer.  From  this  plexus  branches  pass  outward  to  form  a  second 
or  subpapillary  plexus.  From  the  latter,  branches  are  again  given 
off  which,  without  further  anastomoses,  pass  along  beneath  the 
rows  of  papillae  and  supply  each  separate  papilla  with  capillary 
twigs.     These  in  turn  pass  over  into  venous  capillaries  which  unite 

and  form  four  venous 
plexuses,  one  over  the 
other  and  in  general 
parallel  to  the  surface 
of  the  skin.  The  upper- 
most venous  plexus 
lies  beneath  the  pap- 
illae, each  venule  cor- 
responding to  a  single 
row  of  papillae  and 
anastomosing  with  its 
neighbors.  The  sec- 
ond plexus  is  found 
immediately  beneath 
the  first,  the  third  in 
the  lower  portion  of 
the  corium,  and  the 
fourth  at  the  junction 
of  the  cutis  and  sub- 
cutis.  Near  the  mid- 
dle of  the  subcutis  the 
arteries  show  a  circu- 
lar musculature,  but 
the  veins  are  already 
thus  provided  in  the 
network  between  the  cutis  and  subcutis,  where  they  also  seem  to  pos- 
sess valves.  As  already  stated,  the  subcutaneous  fat  is  divided  into 
lobes  by  transverse  and  longitudinal  bundles  of  connective  tissue  ;  a 
second  system  of  bundles  midway  between  the  cutis  and  fascia 
separates  the  panniculus  adiposus  into  an  upper  and  a  lower  layer. 
The  former  is  supplied  by  direct  arterial  branches  ;  the  latter,  by 
branches  passing  backward  from  the  cutaneous  network.  Those 
regions  which  are  subjected  to  great  external  pressure  are  supplied  by 
a  greater  number  of  afferent  vessels  the  caliber  of  which  is  increased. 
In  regions  where  the  skin  is  very  mobile  the  arteries  are  greatly 
convoluted.  All  these  vascular  peculiarities  are  present  in  the  new- 
born (Spalteholz). 

The  lymph-vessels  of  the  true  skin  are  also  distributed  in  two 
layers — a  deep  and  wide-meshed  plexus   in  the   subcutis,   and  a 


Nerve-fibers 
in  the  epi- 
dermis. 

Stratum 
Malpighii. 


Papillae. 


Nerve-fiber. 


Fig.  309. 


-Nerves  of  epidermis  and  papillae  from  ball  of 
cat's  foot ;  X  750' 


THE    SKIN. 


387 


superficial  narrow-meshed  plexus  immediately  beneath  the  papillae. 
Into  the  latter  empty  the  lymph-vessels  coming  from  the  papillae. 
After  treating  the  skin  by  certain  methods,  a  fine  precipitate  may  be 
noticed  here  and  there  in  the  papillary  region  of  the  corium,  a 
proof  that  lymph  clefts  are  present.  These  are  regarded  as  the 
beginnings  of  the  cutaneous  lymphatic  system.  They  may  also  be 
traced  into  the  epithelium,  where  they  are  in  direct  communication 
with  the  interspinal  spaces  between  the  epithelial  cells  (Unna). 
Cells  are  also  met  with  in  the  interspinal  spaces  of  the  epidermis  ; 
these  are  migratory  cells,  or  cells  of  Langerhans. 

The  skin  owes  its  great  sensitiveness  to  the  numerous  nerves 
and  special  nerve-endings  present,  not  only  in  the  epithelium,  but 
also  in  the  corium  and  subcutis.  In  certain  regions  of  the  skin  the 
nerves  have  been  traced  into  the  epithelium.  In  the  finger-tip,  for 
instance,  numerous  nerves  are  seen  in  the  epidermis,  where  they 
branch  and  end  in  telodendria  with  or  without  small  terminal  swell- 
ings.    There  is    no   direct    communication  between   the    terminal 


—  Nen'e-fiber. 


-   Nerve-fiber. 


-  Nerve-fiber. 


Fig.  310.— Meissner' s  corpuscle  from  man  ;       Fig.  31 1.— Meissner' s  corpuscle  from  man  • 

X  750.  X  750. 

nerve  filaments  and  the  epithelial  cells.  (Fig.  309.)  In  certain 
peculiarly  sensitive  regions,  as  the  end  of  the  pig's  snout,  the  nerve- 
fibers  end  in  distinct  saucer-like  discs  (tactile  menisci)  which,  as  a 
rule,  clasp  the  lower  ends  of  the  basal  Malpighian  cells. 

The  special  sensory  nerve-endings  are  situated  in  the  corium 
and  subcutis.  Of  these,  we  ma}'  mention  the  tactile  corpuscles  of 
Meissner,  the  end-bulbs  of  Krause,  the  Pacinian  corpuscles,  Ruf- 
fini's  nerve-endings,  and  the  Golgi-Mazzoni  corpuscles.  All  these 
special  sensory  nerve-endings  wnth  the  exception  of  the  two  last 
mentioned  have  been  discussed  in  a  former  chapter  (p.  169).  Meiss- 
ner's  tactile  corpuscles  are  situated  in  the  tactile  papilla  of  the 
true  skin.      They  are  especially  numerous  in  the  hand  and  foot. 


388 


THE    SKIN    AND    ITS    APPENDAGES. 


In  the  distal  phalanx  of  the  index-finger  every  fourth  papilla  is 
a  tactile  papilla,  containing  one  or  sometimes  two  corpuscles  of 
Meissner.  They  are,  however,  not  nearly  so  numerous  in  other 
parts  of  the  hand  or  in  the  foot.  These  corpuscles  are  further 
found  on  the  dorsal  surface  of  the  hand  and  volar  surface  of  the 
forearm,  in  the  nipple  and  external  genitals,  in  the  eyelids  (border), 
and  in  the  lips.  In  figures  310  and  311  are  shown  two  Meissner's 
corpuscles,  giving  the  appearance  presented  by  these  end-organs 
when  not  stained  with  special  reference  to  nerve  terminations.  For 
the  latter  see  figure  137. 

The  Krause's  end-bulbs,  both  spheric  and  cylindric,  are,  as  a 
rule,  situated  a  short  distance  below  the  papillary  layer,  although 
they  are  frequently  found  in  the  papillae.  They  occur  in  man  in  the 
conjunctiva,  lips,  and  external  genitals,  and  in  the  mucous  mem- 
branes previously  mentioned  (p.  170).  See  page  170  and  figure 
136  for  their  structure. 

In  the  palm  of  the  hand  and  sole  of  the  foot,  the  subcutaneous 
connective  tissue  contains  numerous  Pacinian  corpuscles.  They 
occur  also  along  the  nerve-fibers  of  the  joints  and  in  the  periosteum 
of  the  extremities. 

Very  recently  Ruffihi  demonstrated  in  the  human  corium  the 
existence  of  peculiar  nerve  end-organs,  which  consist  of  a  connec- 
tive-tissue framework  supporting  a  rich  arborization  of  telodendria. 
They  occur  side  by  side  with  the  Pacinian  corpuscles  and  in  appar- 
ently equal  numbers.  These  nerve  terminations  resemble  in  many 
respects  the  neurotendinous  spindles  (see  Fig.  145),  although  they 

present  certain  structural  differences. 
Instead  of  intrafusal  tendon  fasciculi, 
the  Ruffini  end-organ  is  composed 
of  white  fibrous  and  elastic  tissue. 
In  this  end-organ  the  medullated 
nerves  make  long  and  tortuous 
turns  before  becoming  nonmedul- 
lated,  and  the  terminations  of  these 
nerve-fibers  occupy  the  whole  of  the 
cross-section. 

The  Golgi-Mazzoni  corpuscle  re- 
sembles in  structure  the  Pacinian 
corpuscle,  although  it  possesses  fewer 
lamellae  and  a  relatively  larger  core, 
and  the  nerve  -  fibers  terminating 
therein  are  more  extensively  branched 
than  in  the  Pacinian  corpuscle.  Ruf- 
fini has  found  these  nerve-endings  in 
the  subcutaneous  tissue  of  the  finger- 
tips. 

The  blood-vessels  of  the  skin  are  richly  supplied  with  the  vaso- 
motor nerves,  which   terminate   in   the   nonstriated  muscle  of  the 


Terminal  disc  of 
—       nerve-fibers. 


. Epithelial  cell. 

Connective-tissue 

capsule. 


—  Nerve-fiber. 


Fig.  312. — Grandry's  corpuscles  from 
bill  of  duck  ;   X  5^0. 


THE    HAIR.  389 

vessel  walls.      These  vasomotor  nerve-fibers   are  neuraxes  of  s\-m- 
pathetic  neurones. 

In  aquatic  birds,  and  more  especially  in  ducks,  the  waxy  skin  of 
the  beak  and  the  cornified  portion  of  the  tongue  contain  the  so- 
called  corpuscles  of  Herbst,  which  resemble  the  Pacinian  corpuscles 
in  general  structure,  but  have  cubical  cells  in  the  core.  In  the  same 
tissues  are  also  found  the  corpuscles  of  Grandry,  60  [x  long  and 
40  fx  broad.  They  consist  of  a  thin  connective-tissue  capsule,  con- 
taining two  or  three  large  cells.  The  nerve-fiber  retains  its  medul- 
lary sheath  for  some  distance  within  the  capsule.  The  axis-cylinder 
ends  in  discs  situated  between  the  cells  inclosed  by  the  capsule. 

B,  THE  HAIR. 

The  hair  and  nails  are  regarded  as  special  differentiations  of  the 
skin.  Hair  is  found  distributed  over  almost  the  entire  extent  of  the 
skin,  varying,  however,  in  quantity  and  arrangement  in  different 
regions.  None  whatever  is  present  in  the  palm  of  the  hand  and 
sole  of  the  foot.  In  the  third  fetal  month  small  papillary  elevations 
of  the  skin  are  seen  to  develop  in  those  areas  in  which  the  hairy 
growth  later  appears.  Under  each  of  these  elevations  there  occurs 
a  proliferation  of  the  cells  of  the  Malpighian  layer  downward  into 
the  corium.  Although  the  elevations  soon  disappear,  the  epithelial 
ingrowth  continues  and  finally  forms  the  hair  genu.  This  is  soon 
surrounded  by  a  connective-tissue  sheath  from  the  corium,  in  which 
two  layers  may  be  distinguished.  At  the  lower  end  of  the  hair 
germ  the  corium  is  pushed  upward,  forming  a  papilla  which  pene- 
trates into  the  thickened  bulb  of  the  germ.  This  is  called  the  liair 
papilla.  In  the  mean  time  the  hair  germ  itself  is  undergoing  marked 
differentiation.  An  axial  portion,  forming  later  the  hair  and  inner 
root-sheath,  and  a  peripheral,  constituting  later  the  outer  root- 
sheath,  are  developed.  From  the  latter  are  derived  also  the  first 
traces  of  the  sebaceous  glands,  which  in  the  adult  state  are  in  close 
relationship  to  the  hair  and  empty  their  secretion  into  the  space 
between  the  hair  and  its  sheath.  As  soon  as  the  variou's  layers  of 
the  hair  are  complete  it  grows  outward,  breaking  through  the  over- 
lying layers  of  the  epidermis. 

The  visible  portion  of  the  hair  is  called  the  Jiair  shaft,  and 
that  portion  below  the  skin  is  the  hair  root.  The  lower  portion 
of  the  hair  resting  upon  the  papilla  is  known  as  the  Jiair  bulb, 
and  the  sheaths  encircling  the  root  and  bulb  are  called  the  root- 
sheaths,  the  entire  structure  constituting  the  hair  follicle. 

The  adult  hair  is  covered  by  a  thin  cuticle,  consisting  of  over- 
lying plate-like  cells,  i.i  /z  thick,  most  of  which  possess  no  nuclei. 
Beneath  the  cuticle  is  the  cortical  layer,  composed  of  several  strata 
of  long,  flattened  cells  from  4.5  ^m  to  1 1  //  broad  and  provided  with 
nuclei.  These  are  also  known  as  the  cortical  fibers  of  the  hair. 
Upon   treatment   with    ammonia   the    fibers    separate  into  delicate 


390 


THE    SKIN    AND    ITS    APPENDAGES. 


fibrils,  the  hair  fibrils  (Waldeyer,  82).  Scattered  between  and  within 
the  cells  of  the  cortical  layer  are  varying  quantities  of  pigment 
granules.  The  axial  region  of  the  hair  is  occupied  by  the  medullary 
substance,  from  1 6  //  to  20  ;/  in  diameter.  This  may  be  lacking  ;  but 
if  present,  consists  of  from  2  to  4  strata  of  polygonal,  nucleated  and 
pigmented  cells.     The  hair  shaft  often  contains  air  vesicles. 

The  inner  root-sJieatli  consists  of  three  concentric  layers — first, 
of  an  outer  single  layer  of  clear  nonnucleated  cells,  the  so-called 


(/ap 


Fig.  3 1 3. —Transverse  section  of  human  scalp;  X  12:  Ap,  Musculus  arrector  pili ; 
c,  cerium  ;  ep,  epidermis;  fp,  hair  follicle  ;  Gap,  aponeurosis  ;  gh,  sweat-gland  ;  glse,  seba- 
ceous glands ;  KH,  club-hair ;  //,  papilla  of  hair ;  Re,  retinacula  cutis  ;  Rp,  root  of  hau- ; 
Sp,  shaft  of  hair;  ts,  subcutaneous  layer  (Sobotta,  "Atlas  and  Epitome  of  Histology"). 

layer  of  Henle ;  second,  of  a  thicker  middle  layer,  made  up  of  a 
stratum  of  nucleated  cells  containing  keratohyalin,  the  layer  of  Hux- 
ley;  and,  third,  of  an  inner  cuticle,  bordering  upon  the  hair. 

The  outer  root-sheath  is  made  up  of  elements  from  the  stratum 
germinativum.  Here  we  have  to  do  with  prickle  cells,  surrounded 
by  an  outer  layer  of  columnar  elements.  The  connective-tissue 
portion  of  the  hair  follicle  is  composed  of  an  outer,  looser  layer  of 
longitudinal  fibrous  bundles  ;  of  an  inner,  compacter  layer  of  circu- 


THE    HAIR. 


391 


lar  fibers  ;    cind  of  an  innermost  well-developed  Sasement  mem- 
brane— the  glassy  mcnibrane. 

At  a  certain  distance  above  the  root  bulb  all  the  layers  of  the 


The  hair. 


Stratum  Malpighii  of  outer  root-sheath. 


Cuticle  of  hair. 
Cuticle. 


f Inner 
Huxley's  layer.)  root- 

\  sheath. 

_    Henle's  layer.    ' 


-    Glassy  layer. 


Basal  cells  of 
the  outer  root- 
sheath. 


Medulla  of  hail 


Corticalsub- 
stance  of  hair. 


—   Hair  bulb. 


-   Hair  papilla. 
Blood-vessel. 


Glassy  layer  of 
hair  bulb. 


Connective  tis- 
s  u  e  of  the 
cutis. 


Fig.  314. — Longitudinal  section  of  human  hair  and  its  follicle  ;    X  about  300. 


epithelial  portion  of  the  hair  follicle  are  well  developed  and  distinct 
from  each  other.     This  condition  changes  toward  the  hair  papilla 


392 


THE    SKIN    AND    ITS    APPENDAGES. 


as  well  as  toward  the  hair  shaft.  Below,  in  the  region  of  the  thick- 
ened hair  bulb,  the  root-sheaths  begin  to  lessen  in  thickness,  their 
layers  becoming  more  and  more  indistinct  toward  the  base  of  the 
hair  papilla.  Finally,  all  differentiation  is  lost  in  the  region  where 
they  encircle  the  neck  of  the  papilla.  Toward  the  shaft  of  the  hair, 
the  root-sheath  also  undergoes  changes.  In  the  region  into  which 
the  sebaceous  glands  empty,  the  inner  root-sheath  disappears,  while 
the  outer  becomes  continuous  with  the  stratum  germinativum  of 
the  epidermis  ;  the  outer  layers  of  the  latter — the  stratum  granu- 
losum,  stratum  lucidum,  and  stratum  corneum — push  downward 
between  the  outer  root-sheath  and  the  hair  to  the  openings  of  the 
sebaceous  glands. 

Regarding  the  grozvth  of  the  hair,  two  theories  are  prevalent. 


Glassy 
layer. 


Cortex  of 
hair. 

Medulla  of 
hair. 

Cuticle  o  f 
inner  root- 
sheath. 

Henle's 
layer. 

.  Fibrous-tis- 
sue sheath. 


Fig.  3^5 • — Cross-section  of  human  hair  with  its  folHcle  ;  X  about  300. 


The  one  theory  assumes  that  the  elements  destined  to  form  the 
epithelial  root-sheaths  are  derived  from  the  epidermis  by  a  constant 
process  of  invagination.  The  component  parts  of  the  hair  would 
thus  be  continuous  with  the  layers  of  the  root-sheaths,  and  conse- 
quently with  those  of  the  epidermis.  Thus  the  basal  cells  of  the 
external  root-sheath  would  extend  over  the  papilla,  and  be  continu- 
ous with  the  cells  of  the  medulla  of  the  hair  (these  relations  are 
especially  well  defined  in  the  rabbit),  and  the  stratum  spinosum 
(middle  layer  of  stratum  Malpighii)  of  the  outer  root-sheath  would 
be  continuous  with  the  cortical  substance  of  the  hair.  According 
to  this  theory  also,  the  layer  of  Henle  would  correspond  to  the 
stratum   lucidum    of  the   epidermis,  and    at   the   base    of  the    hair 


THE    HAIR. 


393 


Nerve- 

'      plexus  of 

Bonnet. 


would  become  its  cuticle,  while  the  layer  of  Huxley  would  form 
the  cuticle  of  the  inner  root-sheath  (Mertsching).  The  other 
theory  assumes  that  the  hair  is  derived  from  a  matrix,  consisting  of 
proliferating  cells  situated  on  the  surface  of  the  papilla.  From 
these  germinal  cells  would  be  derived  the  medullary  and  cortical 
substance  of  the  hair,  its  cuticle,  and  the  inner  root-sheath  (Unna). 

The  shedding  of  hair  is  common  to  all  mammalia,  a  phenomenon 
occurring  periodically  'm  the  majority  of  species.  In  man  the  pro- 
cess is  continuous.  Microscopic  examination  shows  that  the  hair 
destined  to  be  shed  becomes  loosened  from  its  papilla  by  a  cornifi- 
cation  of  the  cells  of  its  bulb.  At  the  same  time  the  cortical  por- 
tion of  the  hair  bulb  breaks  up  into  a  brush-like  mass.  Such  hairs 
are  called  chib  hairs  or  bidb  hairs,  in  contradistinction  to  papillary 
hairs.  In  the  region  of  the  former 
papilla  there  arises,  by  a  prolifera- 
tion of  the  external  root-sheath,  a 
bud  which  grows  downward,  from 
which  a  new  hair  with  its  sheaths 
and  connective-tissue  papilla  is 
developed.  The  result  is  that  the 
developing  new  hair  gradually 
pushes  the  old  hair  outward  until 
the  latter  finally  drops  out.  The 
exact  details  of  this  process  have 
given  rise  to  considerable  discus- 
sion {via.  Götte  and  Stieda,  87). 

Adjacent  to  the  hair  follicles 
are  bundles  of  smooth  muscle- 
fibers,  known  as  the  arrectorcs  pi- 
loriini.  They  originate  from  the 
papillary  layer  of  the  corium  and 
extend  to  the  lower  part  of  the 
connective -tissue  sheath  of  the  hair 
follicles.  In  their  course  they  not 
infrequently  encircle  the  sebace- 
ous glands  of  the  follicle.     Since 

the  hair  follicles  have  a  direction  oblique  to  the  skin  surface,  forming 
with  it  an  acute  and  an  obtuse  angle,  and  since  the  muscle  is  situated 
within  the  obtuse  angle,  its  function  may  easily  be  conceived  as 
being  that  of  an  erector  of  the  hair.  The  hair  papillae  are  veiy 
vascular. 

The  nerve-fibers  o{  \\\Q.  hair  follicles  have  recently  been  studied  by 
a  number  of  investigators,  with  both  the  Golgi  and  the  methylene- 
blue  methods.  It  has  been  shown  that  the  hair  follicles  receive 
their  nerve  supply  from  the  nerve-fibers  which  terminate  in  the 
immediate  skin  area.  Each  follicle  receives,  as  a  rule,  only  one 
nerve-fiber,  which  reaches  the  follicle  a  short  distance  below  the 
mouth  of  the  sebaceous  gland.     The  nerve-fiber,  on   reaching  the 


Fig.   316 

tlirougli    hair 
■-    160. 


394 


THE    SKIN    AND    ITS    APPENDAGES. 


follicle,  loses  its  medullary  sheath  and  divides  into  two  branches, 
which  surround  it  in  the  form  of  a  ring.  From  this  complete  or 
partial  ring  of  nerve -fibers  numerous  varicose  fibers  proceed  upward 
parallel  to  the  axis  of  the  follicle  for  a  distance  about  equal  to  the 
cross-diameter  of  the  follicle,  to  terminate,  it  would  seem,  largely 
outside  of  the  glassy  layer  (Retzius).  In  certain  mammalia  the 
nerve-fibers  end  in  tactile  discs,  found  in  the  external  root-sheaths 
of  the  so-called  tactile  hairs.  The  muscles  of  the  hairs  receive 
their  innervation  through  the  neuraxes  of  sympathetic  neurones, 
which  reach  the  periphery  from  the  chain  ganglia  through  the  gray 
rami  communicantes.  These  nerves  are  known  as  pilomotor  nerves, 
and  when  stimulated,  excite  contraction  of  the  erector  muscles  of  the 
hairs,  causing  these  to  assume  an  upright  position  and  producing 
the  appearance  termed  goose  skin,  or  cutis  anserina.  Langley 
and  Sherrington  have  made  interesting  and  important  observations 
on  the  course  and  distribution  of  the  pilomotor  nerves. 

C.  THE  NAILS* 

The  nails  are  a  peculiar  modification  of  the  epidermis.     The 
external  arched  portion  is  called  the  body  of  the  nail ;  that  area  upon 


Nail  wall.- 
Nail.- 

Stratum  - 
Malpighii. 

Stratum  cor-- 
neum  of  the 
nail  groove. 


^j;--  Stratum 
.    corneum. 
Stratum 
granulo- 
sum. 
"Cerium. 


--Blood- 

i    vessel. 


Fig-  2)^1  ■ — Longitudinal  section  through  human  nail  and  its  nail  groove 
(sulcus)  ;  X  34- 


which  the  latter  rests,  the  nail  bed,  or  matrix ;  and  the  two  folds  of 
epidermis  which  overlap  the  nail,  the  nail  walls.  The  groove  which 
exists  between  the  nail  wall  and  nail  bed  is  known  as  the  sidcus  of 
the  matrix,  and  the  proximal  imbedded  portion  of  the  nail  as  the 
nail  root,  since  all  growth  of  the  nail  takes  place  in  this  region. 
The  nail  bed  consists  of  the  corium,  which  is  here  made  up  of  a 
dense  felt-work  of  coarse  connective-tissue  fibers.  Immediately 
beneath  the  nail  the  corium  is  raised  into  a  number  of  more 
or  less  symmetric  longitudinal  ridges,  which  again  become  con- 
tinuous with  the  connective-tissue  papillae  of  the  skin  at  the  line 
where  the  nail  projects  beyond  its  bed. 

The  depressions  between  the  ridges  are  occupied  by  epidermal 
cells,  which  also  form  a  thin  covering  over  the  ridges  themselves. 


THE    NAILS.  395 

These  cells  correspond  here  to  the  basilar  layer  of  the  stratum  Mal- 
pighii.  The  stratum  granulosum  is  not  uniformly  present,  although 
occurring  as  isolated  areas  in  the  region  of  the  nail  root  and  lumda, 
the  white  area  of  demilunar  shape  at  the  proximal  portion  of  the 
nail.  Unna  has  demonstrated  that  the  pale  color  of  the  lunula  and 
root  of  the  nail  is  due  to  the  presence  of  keratohyalin.  Formerly, 
this  peculiarity  was  attributed  to  a  difference  in  the  distribution  of 
the  vessels  in  the  various  portions  of  the  nail  bed.  The  body  of 
the  nail,  with  the  exception  of  the  lunula,  is  transparent — a  con- 
dition which  may  be  explained  by  the  fact  that  the  elements  of  the 
nail  correspond  to  those  of  the  stratum  lucidum.  As  a  consequence, 
the  vessels  of  the  matrix  shine  through,  except  at  the  lunula,  where 
the  keratohyalin  granules  render  the  nail  opaque. 

The  nail  itself  consists  of  elements  homologous  to  those  of  the 
stratum  lucidum.  They  are  flat,  transparent  cells,  closely  approxi- 
mated, and  all  contain  nuclei.  The  cells  overlie  each  other  like 
tiles,  and  are  so  arranged  that  each  succeeding  lower  layer  projects 

Nail.-<--- 
Stratum  Mai- •*  --    ^^ 

pighii. 
Nail  wall  - 

Nail  groove., 

J  ,  — Corium. 

\  ~-  ^  —Blood-vessel. 


Fig.  318. — Transverse  section  through  human  nail  and  its  sulcus  ;  X  34- 

a  little  further  distalward  than  the  preceding.  At  the  period  when 
the  nails  are  formed,  about  the  fourth  month  of  fetal  life,  sulci  are 
already  present.  The  first  trace  of  the  nail  is  seen  as  a  marked 
thickening  of  the  stratum  lucidum  in  the,  region  which  later  be^- 
comes  the  body  of  the  nail ;  in  this  stage  the  structure  is  still  cov- 
ered by  the  remaining  layers  of  the  stratum  corneum,  constituting 
the  eponycliiinn.  The  embryonal  nail  then  spreads  in  all  directions 
until  it  finally  reaches  the  sulcus.  Henceforward  the  growth  is 
uniform.  The  eleidin  normally  present  in  the  stratum  lucidum  of 
the  skin  also  occurs,  in  the  nail,  and  is  derived,  as  we  have  already 
seen,  from  the  keratohyalin.  It  may  readily  be  conceived  that  later, 
when  growth  is  confined  to  the  root  of  the  nail,  keratohyaHn  is  also 
present.  As  soon  as  the  nail  begins  to  grow  forward,  in  the  ninth 
month,  the  greater  part  of  the  eponychium  is  thrown  off;  but 
during  the  entire  extrauterine  life,  a  portion  of  the  eponychium  is 
retained  at  the  nail  wall,  and  as  hyponychium  on  the  anterior  and 
under  surface  of  the  nail. 


396 


THE    SKIN    AND    ITS    APPENDAGES. 


D.  THE  GLANDS  OF  THE  SKIN. 

The  glands  in  the  skin  are  of  two  kinds — sweat-glands  and 
sebaceous  glands.  In  this  connection  we  may  also  consider  the 
mammary  glands,  which  may  be  regarded  as  a  modified  skin  gland. 

I.    The   Sweat-glands. — The   sweat-glands,  or  sudoriparous 


Fig.  319.  — A,  B,  Two  views  of  a  model  of  the  coiled  portion  of  a  sweat-gland 
from  the  plantar  region  of  a  man,  reconstructed  by  Born's  wax-plate  method  ;  X  ^^o 
( Huber- Adamson) . 


glands,  are  distributed  throughout  the  entire  skin,  but  are  especially 
numerous  in  certain  regions — as,  for  instance,  the  axilla,  palm  of 
the  hand,  and  sole  of  the  foot.  They  lie  imbedded  either  in  the 
adipose  tissue  of  the  true  skin,  or  still  deeper  in  the  subcutaneous 
connective  tissue. 

The  sweat-glands  are  simple  tubular  in  type,  and  their  secreting 

portion  is  coiled  ;  hence 
the  name  coil-glands. 
The  coiled  portion  of 
these  glands  measures 
0.3  to  0.4  mm.  The 
excretory  duct  is  nearly 
straight  in  its  course 
through  the  corium. 
From  here  on  its  course 
is  spiral,  and  it  should 
be  borne  in  mind  that  in 
its  passage  through  the 
epidermis  it  has  no  other 
wall  than  the  epidermal 
cells  of  the  various  lay- 
ers through  which  it 
passes,  although  these 
cells  are  arranged  con- 
centrically around  the  lumen  of  the  duct.  The  duct  takes  part  in 
the  formation  of  the  coiled  portion  of  the  gland,  forming  about  one- 
fourth  of  the  length  of  the  tubule  which  takes  part  in  the  formation 


Basement 
membrane. 


Nonstriated 
muscle-cell. 


Gland-cell. 


Fig.  320. — Cross  -  section  of  tubule  of  coiled 
portion  of  sweat-gland  of  human  axilla.  Fixation 
with  sublimate  ;   X  ^OO- 


THE    GLANDS    OF    THE    SKIN. 


397 


Nucleus  of 
nonstriated 
muscle-cell. 


Nucleus  of 
gland-cell. 


of  the  coil.  In  figure  319  are  shown  two  views  of  a  model  of  the 
coiled  portion  of  a  sweat-gland  from  the  plantar  region  of  the  foot 
of  a  man.  The  length  of  the  tubule  in  the  coiled  portion  of  this 
gland  measures  4.25  mm.,  of  which  1.25  mm.  fall  to  the  excretoiy 
duct  and  3.0  mm.  to  the  secretory  tubule. 

The  blind  end  of  the  secreting  portion  of  the  tubule  and  the  ex- 
cretory duct  as  it  enters  the  coil  are  usually  in  close  proximity. 
The  secretory  portion  of  the  tubule  of  sweat-glands  is  lined  by  a 
single  layer  of  cubic  or  columnar  cells,  with  finely  granular  proto- 
plasm and  round  or  oval  nuclei  possessing  one  or  two  nucleoli.  Be- 
tween this  layer  of  cells  and  the  basement  membrane  there  is  found 
a  layer  of  nonstriated  muscle-cells,  longitudinally  disposed.  The 
portion  of  the  excretory  duct  found  within  the  coil  of  the  glands 
is  lined  by  a  single  layer  of  short  cubic  cells,  with  cuticular  border, 
outside  of  which  there  is  a  delicate  basement  membrane.  The 
muscular  layer  is  lacking  in 
this  and  the  remaining  portion 
of  the  duct.  The  excretory 
portion  of  the  duct  passing 
through  the  corium  is  lined 
by  short,  somewhat  irregu- 
larly cubic  cells  arranged  in 
two  layers. 

Capillary  networks  sur- 
round the  secreting  portions 
of  the  sweat-glands. 

The  nerves  of  the  sweat- 
glands  have  been  studied  with 
the  aid  of  the  methylene-blue 
method  by  Ostroumow,  work- 
ing under  Arnstein's  direction. 
These  glands  receive  their  in- 
nervation through  the  neur- 
axes  of  sympathetic  neurones, 

the  terminal  branches  of  which  form  an  intricate  network  just  out- 
side of  the  basement  membrane,  known  as  the  epilamelhv  plexus. 
From  this  plexus  fine  varicose  nerve-fibers  pass  through  the  base- 
ment membrane,  and,  after  coursing  a  shorter  or  longer  distance 
with  or  without  further  division,  end  on  the  gland-cells,  often  in 
clusters  of  small  terminal  granules  united  by  delicate  threads. 

The  development  of  the  sweat-glands  begins  in  the  fifth  month 
of  fetal  life.  At  first  solid  cords  grow  from  the  stratum  germi- 
nativum  of  the  epidermis  into  the  corium.  Later,  in  the  seventh 
month,  these  become  hollow. 

Joseph  has  shown  a  structural  change  in  the  secretor\^  cells 
of  the  sweat-glands  when  perspiration  was  induced  by  electrical 
stimulation  or  by  drugs. 

With   the  sweat-glands  as  here  described,  and  which  have,  as 


Fig.  321. — Tangential  section  through 
coiled  portion  of  sweat-gland  from  human 
axilla.      Sublimate  fixation  ;    X  700- 


398 


THE    SKIN    AND    ITS    APPENDAGES. 


has  been  stated,  a  very  wide  distribution,  we  may  also  class  certain  skin 
glands,  grouped  under  the  term  of  "modified  sweat-glands,"  which 
show  certain  structural  and  morphologic  peculiarities  and  are  found 
in  special  regions  of  the  body.  To  these  belong  the  axillary 
glands,  the  circumanal  glands,  the  ciliary  glands  or  glands  of 
Moll  of  the  eyelid,  and  the  ceruminous  glands  of  the  external 
auditory  canal.  The  axillary  glands  resemble  the  sweat-glands  in 
shape  and  structure,  possessing,  however,  larger  and  longer  tubules. 
The  coiled  portions  of  these  glands  measure  1.5  to  2  mm.,  the 
tubule  of  the  coil  attaining  a  length  of  30  mm.  In  the  circumanal 
region  are  found  several  types  of  sweat-glands,  especially  in  an 
area  having  the  form  of  an  elliptical  ring  with  a  width  of  about  1.5 
cm.  and  situated  about  1.5  cm.  from  the  anus.     In  this  region  there 


Fig.  322. — Model  of  a  sebaceous  gland  with  a  portion  of  the  hair  follicle,  reconstructed 
by  Born's  wax-plate  method.      A,  Hair  follicle. 


are  found  large  sweat-glands,  known  as  the  circumanal  glands  of 
Gay;  branched  sweat-glands  of  the  type  of  tubulo-alveolar  glands  ; 
sweat-glands  with  relatively  straight  ducts,  ending  in  a  relatively 
large  saccule  or  vesicle,  from  which  arise  secondary  tubules  or 
alveoli;  and,  finally,  sweat-glands  of  the  type  as  found  in  other 
regions  of  the  body.  The  ciliary  glands  or  glands  of  Moll  may 
also  be  classed  as  branched  glands  of  the  type  of  tubulo  -alveolar 
glands,  with  relatively  large  vesicles.  The  ceruminous  glands  are 
branched  tubulo-alveolar  glands. 

2.  The  Sebaceous  Glands. — The  distribution  of  the  sebaceous 
glands  in  the  skin  is  closely  connected  with  that  of  the  hair  follicles 
into  which  they  pour  their  contents.      Exceptions  to  this  rule  occur 


THE  GLANDS  OF  THE  SKIN. 


399 


in  only  a  few  regions  of  the  body,  as,  for  instance,  in  the  glans  penis 
and  foreskin  (Tyson's  glands),  in  the  labia  minora,  angle  of  the 
mouth,  glandule  tarsales,  and  the  Meibomian  glands  of  the  eyelids, 
etc.  As  a  rule  the  sebaceous  gland  empties  by  a  wide  excretory 
duct  into  the  upper  third  of  the  hair  follicle.  The  walls  of  the  duct 
also  produce  secretion,  and  can  therefore  hardly  be  differentiated 
from  the  rest  of  the  gland.  At  its  base  the  duct  widens  and  is  pro- 
vided with  a  number  of  simple  or  branched  alveoli.  The  sebaceous 
glands  are  therefore  of  the  type  of  simple  branched  alveolar  glands, 
varying  in  length  from  0.2  mm.  to  0.5  mm.  They  are  surrounded 
by  connective-tissue  sheaths,  which  at  the  same  time  cover  the  hair 
follicles.  Inside  of  the  sheath  is  the  membrana  propria,  which  is  a 
continuation  of  the  glassy  membrane  of  the  follicle.  The  two  or 
three  basal  strata  of  glandular  cells  must  be  regarded  as  a  direct 
continuation  of  the  elements  of  the  external    root-sheath.      In  the 


Fig.  323. — Section  of  alveoli  from  sebaceous  gland  of  human  scalp. 


more  centrally  placed  strata  the  cells  are  distinctly  changed  in  char- 
acter ;  their  contents  consist  of  fat  globules,  varying  in  size  and 
distributed  throughout  the  protoplasm,  giving  this  a  reticular 
appearance,  while  the  nuclei  suffer  compression  from  the  accumu- 
lation of  the  fat  globules  and  gradually  become  smaller  and  more 
angular.  Finally,  the  cells  change  directly  into  secretion,  which  is 
then  poured  into  the  hair  follicle  as  sebum.  It  is  thus  seen  that  in 
the  secretion  of  sebum  the  cells  are  consumed  and  must  be  re- 
placed. This  renewal  takes  place  by  the  constant  proliferation 
of  the  basilar  cells,  which  push  the  remains  of  the  secreting  cells 
upward  and  finally  take  their  places.  The  final  disintegration  of  the 
cells  occurs  either  within  the  gland  itself  or  between  the  hair  follicle 


400  THE    SKIN    AND    ITS    APPENDAGES. 

and  the  hair.      The  secretion  contains  fatty  globules  of  varying  size, 
which  occur  either  free  or  attached  to  cellular  detritus. 

3.  The  Mammary  Glands. — The  mammary  glands  are  also 
included  among  the  cutaneous  glandular  structures.  They  are 
developed  early,  but  not  until  the  fifth  month  is  it  possible  to  dis- 
tinguish a  solid  central  portion,  with  radially  arranged  tubules 
terminating  in  dilatations.  The  structures  are  all  derived  from  the 
basal  layers  of  the  epidermis.      From  birth  to  the  age  of  puberty 


Fig.    324.  — Model  of  a  small  portion  of  a  secreting  mammary  gland;   X  200. 
( Maziarski,  Anatomische  Hefte,  vol.  XVlll.j 

the  organs  are  in  a  state  of  constant  growth,  and  are  early  sur- 
rounded by  a  connective-tissue  sheath.  The  alveoli,  which  have 
been  developed  in  the  mean  time,  are  still  solid  and  relatively  small. 
Up  to  the  twelfth  year  the  glands  remain  identical  in  structure 
in  boys  and  girls.  In  the  female  the  mammary  glands  continue  to 
develop  from  the  age  of  puberty  ;  in  the  male,  on  the  other  hand, 
they  undergo  a  retrograde  metamorphosis,  ending,  finally,  in  the 
atrophy  of  all  except  the  excretory  ducts.  The  mammary  glands 
do  not  attain  their  full  stage  of  development  in  women  until  the 
last  months  of  pregnancy,  and  are  functionally  active  at  parturition. 
The  human  mammary  gland  when  fully  developed  has  the  fol- 
lowing structure  :  It  consists  of  about  twenty  lobes,  separated  from 
each  other  by  connective-tissue  septa.  These  lobes  are  again 
divided  into  a  larger  number  of  lobules,  and  these  in  turn  are  com- 
posed of  numerous  irregularly  round  or  oval  or  even  tubular  al- 
veoli. The  alveoli  are  provided  with  small  excretory  passages, 
which  unite  to  form  the  smaller  ducts,  these  in  turn  uniting  to  form 
the  larger  ducts.  Shortly  before  terminating  at  the  surface  of  the 
mammilla,  each  mammary  duct  widens  into  a  vesicle,  the  sinus 
lactiferus.  The  number  of  excretory  ducts  corresponds  to  that 
of  the  larger  lobes.      The  ducts  are  Hned  by  simple  cubical  epithe- 


THE    GLANDS    OF    THE    SKIN. 


401 


lium,  except  near  their  termination  in  the  nipple,  where  they  are 
lined  by  stratified  pavement  epithelium,  and  surrounded  by  a  fibrous 
tissue  sheath. 

The  epithelium  of  the  alveoli  differs  according  to  the  state  of 
functional  activity.  In  a  state  of  rest  it  consists  of  a  single  layer 
of  glandular  cells  of  nearly  cubical  shape  which  stain  deeply,  the 
internal  surfaces  now  and  then  projecting  slightly  into  the  lumen. 
At  the  beginning  of  secretion  fat  globules  make  their  appearance  in 
the  distal  ends  of  the  cells.     At  the  same  time  a  corresponding 


eolus. 


Duct  and 
alveoli. 


Adipose  tissue. 

Fig.   325. — From   section  of  mammary  gland  of  nullipara.      (From    Nagel's   "Die 
weiblichen  Geschlechtsorgane,"  in   "Handbuch  der  Anatomie  des  Menschen,"    1896.) 


increase  in  size  occurs  throughout  the  entire  alveolus.  There  are 
as  yet  current  two  quite  contradictoiy  views  as  to  the  manner  in  which 
the  milk  is  secreted.  According  to  certain  observers,  the  free  ends 
of  the  cells,  which  contain  the  most  fat  globules,  are  constricted  off, 
after  which  the  fat  globules  are  freed  in  the  lumen.  The  secretory 
portion  of  the  alveolus  is  then  composed  of  low  epithelial  cells,  in 
which  the  process  begins  anew.  The  process  of  milk  secretion 
therefore  consists  in  throwing  off  the  inner  halves  of  the  cells  con- 
taining the  fat  globules,  and  in  regeneration  of  the  cells  from  the 
26 


402  THE    SKIN    AND    ITS    APPENDAGES. 

nucleated  remains  of  the  glandular  epithelium.  Whether  a  karyokin- 
etic  division  of  the  nuclei  occurs  in  this  process  is  not  known,  and 
how  often  the  process  of  regeneration  may  be  repeated  in  a  single 
cell  is  not  capable  of  demonstration.  It  is  certain,  however,  that 
entire  cells  are  destroyed,  to  be  replaced  later  by  new  elements. 
Other  observers  regard  the  secretion  of  milk  as  occurring  without  a 
partial  or  total  destruction  of  the  secretory  cells,  but  after  the  manner 
of  the  secretion  of  other  glands.  This  latter  view  seems  more  in 
accord  with  the  more  recent  observations.  The  membrana  propria 
of  the  alveoli  appears  homogeneous.  Between  it  and  the  glandular 
cells  are  so-called  basket  cells,  similar  to  those  in  the  salivary 
glands,  Benda  regards  the  basket  cells  as  nonstriated  muscle 
elements  having  a  longitudinal  direction,  making  the  structure  of 
the  alveoli  of  the  mammary  gland  similar  in  this  respect  to  that  of 
the  secreting  portion  of  the  sweat-glands. 

The  skin  of  the  mammilla  is  pigmented,  and  the  papillae  of  its 
corium  are  very  narrow  and  long.  In  the  corium  are  also  found 
large  numbers  of  smooth  muscle-fibers,  which  form  circular  bun- 
dles around  the  excretory  ducts.  In  the  areolae  of  the  mammae 
are  the  so-called  glands  of  Montgomery,  which  very  probably  repre- 
sent accessory  mammary  glands.  These  are  especially  noticeable 
during  lactation.  The  blood-vessels  of  the  mammary  gland,  the 
larger  branches  of  which  are  situated  mainly  in  the  subcutaneous 
tissue,  form  rich  capillary  networks  about  the  alveoli. 

The  mammary  glands  possess  many  lymphatics.  These  are 
especially  numerous  in  the  connective-tissue  stroma  between  the 
lobules.  The  lymph-vessels  collect  to  form  two  or  three  larger 
vessels,  which  empty  into  the  axillary  glands.  The  mammary 
gland  receives  its  nerve  supply  from  the  sympathetic  and  cerebro- 
spinal nervous  systems  through  the  fourth,  fifth,  and  sixth  inter- 
costal nerves.  The  terminations  of  the  nerves  in  the  mammary 
gland  have  been  studied  by  means  of  the  methylene-blue  method 
by  Dmitrewsky,  working  in  the  Arnstein  laboratory,  who  finds  that 
the  terminal  branches  form  epilamellar  plexuses  outside  of  the 
basement  membrane  of  the  alveoli,  from  which  fine  nerve  branches 
pass  through  the  basement  membrane  and  end  on  the  gland  cells 
in  clusters  of  terminal  granules  united  by  fine  filaments.  The 
nipple  has  a  rich  sensory  nerve  supply.  In  the  connective-tissue 
papillae  are  found  tactile  corpuscles  of  Meissner. 

The  milk  consists  of  fat  globules  of  varying  size,  which,  how- 
ever, do  not  coalesce — an  attribute  due  to  the  presence  of  albu- 
minous haptogenic  membranes  surrounding  the  globules.  Shortly 
before,  and  for  some  days  after,  parturition  the  milk  contains  true 
nucleated  cells  in  which  are  fat  globules  ;  these  are  known  as  the 
colostrum  corpuscles.  They  probably  represent  leucocytes  which 
have  migrated  into  the  lumen  of  the  gland  and  have  taken  up  the 
fat  globules  of  the  milk.      This  milk  is  known  as  colostrum. 


TECHNIC.  403 


TECHNIC. 


Good  general  views  of  the  skin  can  be  obtained  only  from  sections. 
Any  fixation  method  may  be  employed,  although  alcohol  is  preferable  on 
account  of  the  better  subsequent  staining.  For  detail  work  Flemming's 
solution,  corrosive  sublimate,  or  osmic  acid  is  the  best.  Sectioning  of  the 
skin  is  attended  with  many  difficulties,  and  large  pieces  can  be  cut  only 
in  celloidin.  Small  and  medium-sized  pieces  may  be  cut  in  paraffin  ;  but 
even  in  this  case  the  skin  must  be  rapidly  imbedded  in  the  paraffin — /.  e., 
it  must  not  remain  too  long  in  either  alcohol  or  toluol — and  the  paraffin 
must  have  only  the  consistency  necessary  to  cut  well  (about  50°  C.  melting- 
point).  In  order  to  obtain  good  paraffin  sections  of  the  skin  the  follow- 
ing procedure  is  recommended  :  Pieces  fixed  in  Flemming's  solution  or 
osmic  acid  are  kept  in  96%  alcohol,  then  placed  for  not  more  than  twenty- 
four  hours  in  absolute  alcohol  and  imbedded  in  paraffin  by  means  of  the 
chloroform  method.  In  the  chloroform,  chloroform -paraffin,  and  pure 
paraffin  they  remain  for  one  hour  each.  The  paraffin  used  should  consist  of 
two  parts  paraffin  of  42°  C. ,  and  one  part  paraffin  of  50°  C.  melting-point. 
The  thermostat  must  be  kept  at  50°  C.  (R.  Barlow).  The  sections 
should  not  be  mounted  by  the  water-albumen  method. 

In  sections  of  epidermis  which  have  been  freshly  fixed  with 
osmic  acid,  the  stratum  corneum  may  be  clearly  differentiated  into  three 
layers  (probably  because  of  the  defective  penetration  of  the  reagent) — 
into  a  blackened  superficial,  a  middle  transparent,  and  a  still  lower  black 
layer  {vid.  Fig.  326). 

In  tissue  fixed  in  alcohol  or  corrosive  sublimate  the  stratum 
lucidum  stains  yellow  with  picrocarmin,  but  is  very  weakly  colored  by 
basic  anilin  stains.  In  unstained  preparations  the  stratum  lucidum  is 
glass-like  and  transparent.  Eleidin  is  diffusely  scattered  throughout  both 
the  stratum  lucidum  and  stratum  corneum.  Like  keratohyalin,  it  stains 
with  osmic  acid  and  also  with  picrocarmin,  but  not  with  hematoxylin. 
Nigrosin  stains  eleidin,  but  not  keratohyalin. 

Keratohyalin  is  insoluble  in  boiling  water  and  is  not  attacked 
by  weak  organic  acids.  It  dissolves,  however,  in  boiling  acetic  acid,  but 
is  not  changed  by  the  action  of  pepsin  or  trypsin.  The  keratohyalin 
granules  of  the  stratum  granulosum  swell  in  from  1%  to  5%  potassium- 
hydrate  solution  ;  under  the  influence  of  heat  these  granules  together  with 
the  cells  containing  them  are  finally  dissolved.  They  are  not  attacked 
by  ammonia,  and  remain  unaffected  for  a  long  time  in  strong  acetic  acid. 
As  ammonia  and  acetic  acid  render  the  remaining  portions  of  the  tissue 
transparent,  these  reagents  may  be  employed  for  the  rapid  identification 
of  keratohyalin.  The  larger  flakes  of  keratohyalin  swell  in  sodium  car- 
bonate solution  (1%),  but  not  the  smaller  granules,  and  it  would  seem 
that  the  larger  granules  have  less  power  of  resistance  than  the  smaller. 
Keratohyalin  remains  unchanged  in  alcohol,  chloroform,  and  ether,  but 
is  digested  in  trypsin  and  pepsin  (not,  however,  the  keratin).  Kerato- 
hyalin can  be  stained  with  hematoxylin  and  most  of  the  basic  anilin  dyes. 

The  prickles  of  the  cells  composing  the  stratum  Malpighii  may 
be  seen  in  very  thin  sections  (not  over  3  //  in  thickness)  of  skin  previ- 
ously fixed  in  osmic  acid.  In  this  case  it  is  best  to  employ  not  Canada 
balsam,  but  glycerin,  which  does  not  have  so  strong  a  clearing  action. 
Isolation  of  the  prickle  cells  is  best  accomplished  as  follows  (Schiefifer- 


404 


THE    SKIN    AND    ITS    APPENDAGES. 


decker) :  A  fresh  piece  of  epidermis  is  macerated  for  a  few  hours  in 
filtered,  cold-saturated,  aqueous  solution  of  dry  pancreatin  ;  the  whole 
may  then  be  preserved  for  any  length  of  time  in  equal  parts  of  glycerin, 


Outer  dark  layer. 

-    Stratum  corneum. 
Middle  light  layer. 

"  Inner  dark  layer. 
"  Stratum  lucidum. 

Stratum  Malpighii. 


If; 


N^ 


'e: 


»^ 


C 


Cutis  and  sub- 
cutis. 


Fat  cell. 


Fig.  326. — Transverse  section  through  the  human  skin.  Treated  with  osmic  acid  ; 
X  30  :  a,  Part  of  the  tortuous  duct  of  a  sweat-gland  in  the  epidermis  ;  b,  duct  of  same 
sweat-gland  in  the  corium. 


water,  and  alcohol.  Small  pieces  taken  from  such  specimens  are  readily 
teased  and  show  both  isolated  and  small  groups  of  attached  prickle  cells. 

The  distribution  of  the  pigment  in  the  skin  is  best  studied  in 
unstained  sections.  With  a  nearly  closed  diaphragm  and  under  medium 
magnification  the  pigment  granules  appear  darker  on  raising  the  tube  and 
lighter  upon  lowering  it. 

In  sections  of  skin  treated  with  Flemming's  fluid,  the  structure 
of  the  cutis  also  may  be  studied.  The  medullary  sheaths  of  the  nerve- 
fibers  and  the  fat  appear  black.  In  preparations  stained  with  safranin  the 
elastic  fibers  are  colored  red  and  are  very  distinct  (Stöhr  and  O. 
Schul tze).     For  the  orcein  method  according  to  Unna,  see  p.  128. 

Hair  may  be  examined  in  water  without  further  manipulation. 
The  cuticle  is  then  seen  to  consist  of  polygonal  areas,  the  border-lines  of 
which  correspond  to  the  limits  of  the  flattened  cells.  By  slightly  lower- 
ing the  objective  the  cortical  substance  comes  into  view  with  its  indistinct 


TECHNIC.  405 

striation  and  occasional  pigmentation.  The  medullary  substance,  if  pres- 
ent, may  also  be  seen  with  its  vesicles  containing  air.  Both  the  cortical 
and  cuticular  cells  may  be  isolated,  the  process  consisting  in  treating  the 
hairs  for  several  days  with  33  '^  potassium  hydrate  solution  at  room  tem- 
perature, or  in  heating  the  whole  for  a  few  minutes.  Concentrated  or 
weak  sulphuric  acid  produces  the  same  result.  On  warming  a  hair  in  sul- 
phuric acid  until  it  begins  to  curl  and  then  examining  it  in  water,  we  find 
that  the  cortical  and  medullary  layers  as  well  as  the  cuticle  are  separated 
into  their  elements.  Treatment  of  the  skin  with  Müller' s  fluid,  alco- 
hol, or  sublimate  is  recommended  for  the  examination  of  hair  and  hair 
follicles.  The  orientation  of  the  specimen  should  be  very  precise,  in 
order  to  obtain  exact  longitudinal  or  cross-sections  of  the  hair.  There 
is  hardly  a  structure  of  the  body  which  is  more  suitable  for  staining 
with  the  numerous  coal-tar  colors  than  the  hair  and  its  follicle  (Merkel). 

The  corpuscles  of  Meissner  may  be  best  obtained  from  the  end 
of  the  finger.  After  boiling  a  piece  of  fresh  skin  from  the  finger-tip  for 
about  a  quarter  of  an  hour,  the  epidermis  may  be  easily  removed  ;  the 
papillae  are  now  seen  on  the  free  surface  of  the  cutis.  A  portion  of  the 
latter  is  cut  away  with  a  razor  and  examined  in  a  3  %  solution  of  acetic 
acid.  The  corpuscles  are  readily  distinguished.  Their  relations  to  the 
nerves  should  he  studied  in  specimens  fixed  with  osmic  acid  or  gold 
chlorid.  The  terminations  of  the  nerves  in  these  end-organs  are  best  seen 
in  preparations  stained  after  the  m^ra  vitam  methylene-blue  method. 

The  corpuscles  of  Herbst  and  Grandry  are  found  in  the  waxy 
skin  covering  the  bill,  and  in  the  palate  of  the  duck  (especially  numerous 
in  the  tongue  of  the  woodpecker) .  For  the  study  of  the  nervous  ele- 
ments the  following  method  is  useful  :  Pieces  of  the  waxy  skin  are 
removed  with  a  razor  and  placed  for  twenty  minutes  in  50%  formic  acid. 
After  washing  the  specimens  for  a  short  time  in  distilled  water  they  are 
transferred  to  a  small  quantity  of  1%  gold  chlorid  solution  (twenty  min- 
utes), then  again  rinsed  in  distilled  water,  and  placed  for  from  twenty- 
four  to  thirty-six  hours  in  the  dark  in  a  large  quantity  (^  liter)  of 
Pichard's  solution  (amyl  alcohol  i  part,  formic  acid  i  part,  water  100 
parts).  After  again  washing  in  water  the  specimens  are  transferred  to 
alcohols  of  gradually  increasing  strengths  and  finally  imbedded  in  celloidin 
or  celloidin-paraffin. 

The  Pacinian  corpuscles  occur  in  the  mesentery  of  the  cat  and 
may  be  examined  in  physiologic  saline  solution. 

The  nerves  of  the  epidermis  are  demonstrated  by  the  gold- 
chlorid  method  (see  p.  48).  But  even  here  the  chrome-silver  method  and 
the  mtra  vitam  methylene-blue  method  yield  extremely  good  results,  and 
may  be  used  with  great  advantage  in  the  study  of  the  nerves  in  the  cutis. 

The  so-called  tactile  menisci  are  very  numerous  in  the  snout  of 
the  pig  and  the  mole.  Bonnet  recommends  for  these  structures  fixation  in 
0.2,2,%  chromic  acid  solution,  overstaining  with  hematoxylin,  and  differ- 
entiation in  an  alcoholic  solution  of  potassium  ferricyanid. 


406  THE    CENTRAL    NERVOUS    SYSTEM. 


VII.  THE  CENTRAL  NERVOUS  SYSTEM. 

In  a  study  of  the  minute  anatomy  of  the  central  nervous  system 
consideration  should  be  given  to  the  arrangement  of  the  nerve-cells 
and  nerve-fibers  in  the  various  regions,  and  to  the  mutual  relations 
which  the  elements  of  the  nervous  system  bear  to  one  another.  In 
a  text-book  of  this  scope,  however,  we  shall  be  unable  to  enter  into 
the  consideration  of  these  subjects  in  detail,  but  must  content  our- 
selves with  a  very  general  discussion  of  the  structure  of  certain 
regions  of  the  central  nervous  system  and  an  account  of  a  few  typical 
examples  illustrating  the  mutual  relationship  of  the  nerve-elements 
to  one  another.  We  shall,  therefore,  give  a  general  description  of 
the  structure  of  the  spinal  cord,  cerebellum,  cerebrum,  olfactory 
lobes,  and  ganglia.  In  this  description  we  have  drawn  freely 
from  the  results  of  the  researches  of  Golgi  (94),  Ramon  y  Cajal 
(93,  i),  von  Lenhossek  (95),  Kölliker  (93),  and  van  Gebuchten 
(96). 

A.  THE  SPINAL  CORD. 

The  spinal  cord  extends  from  the  upper  border  of  the  atlas  to 
about  the  lower  border  of  the  first  lumbar  vertebra.  It  has  the  form 
of  a  cylindric  column,  which  at  its  lower  end  becomes  quite  abruptly 
smaller,  to  form  the  comis  medtdlaris,  and  terminates  in  an  attenu- 
ated portion — the  ßhcm  terminale.  It  presents  two  fusiform  enlarge- 
ments, known  as  the  cervical  and  lumbar  enlargements  respectively. 
The  spinal  cord  is  partly  divided  into  two  symmetric  halves  by  an 
anterior  median  fissure  and  by  a  septum  of  connective  tissue,  extend- 
ing into  the  substance  of  the  cord  from  the  pia  mater  (one  of  the 
fibrous  tissue  membranes  surrounding  the  cord),  and  known  as  the 
posterior  median  septum.  Structurally  considered,  the  spinal  cord 
consists  of  white  matter  (mainly  medullated  nerve-fibers)  and  gray 
matter  (mainly  nerve-cells  and  medullated  nerve- fibers).  The  white 
and  the  gray  matter  present  essentially  the  same  general  features  at 
ail  levels  of  the  spinal  cord,  although  the  relative  proportion  of  the 
two  substances  varies  somewhat  at  different  levels.  The  different 
portions  of  the  cord  present  also  certain  structural  peculiarities. 

The  distribution  of  the  gray  and  the  white  substances  of  the 
spinal  cord  is  best  seen  in  transverse  sections. 

The  varying  shape  of  the  spinal  cord  in  the  several  regions  and 
the  changing  relations  of  the  gray  to  the  white  substance  are  shown 
in  the  illustrations  of  cross-sections  of  the  adult  human  spinal 
cord  (see  p.  407). 

The  gray  substance  is  arranged  in  the  form  of  two  crescents, 
one  in  each  half  of  the  cord,  united  by  a  median  portion  extending 
from  one  half  of  the  cord  to  the  other,  the  whole  presenting  some- 
what the  form  of  an  H.     The  horizontal  part  contains  the  commis- 


THE    SPINAL    CORD. 


407 


Fig.  327. — Four  cross-sections  of  the  human  spinal  cord  ;  X  7  — '^>  Cervical  region 
in  the  plane  of  the  sixth  spinal  nerve-root  ;  B,  lumbar  region  ;  C,  thoracic  region  ;  Z>, 
sacral  region  (compare  with  Fig.  328).     (From  preparations  of  H.  Schmaus.) 


408  THE    CENTRAL    NERVOUS    SYSTEM. 

sures  and  the  central  canal  of  the  spinal  cord,  while  the  vertical 
limbs  or  crescents  extend  to  the  ventral  and  dorsal  nerve-roots, 
forming  the  anterior  and  posterior  horns.  The  former  are,  as  a 
rule,  the  larger,  and  at  their  sides  (laterally)  the  so-called  lateral 
horns  may  be  seen,  varying  in  size  in  different  regions.  In  each 
anterior  horn  are  three  main  groups  of  ganglion  cells  :  the  ventro- 
lateral, made  up  of  root  or  motor  nerve-cells  ;  the  ventromesial, 
composed  of  commissural  cells  ;  and  the  lateral  (in  the  lateral 
horn),  containing  column  cells.  At  the  median  side  of  the  base 
of  each  posterior  horn  we  find  a  group  of  cells  and  fibers  known 
as  the  column  of  Clark,  most  clearly  defined  in  the  dorsal  region, 
while  in  the  posterior  horn  itself  is  the  gelatinous  Substance  of 
Rolando.  Aside  from  these,  numerous  cells  and  fibers  are  scat- 
tered throughout  the  entire  gray  substance. 

The  motor  nerve-cells  lie  in  the  ventrolateral  portion  of  the  ante- 
rior horn,  their  neuraxes  extending  into  the  anterior  nerve-root. 
Their  dendrites  are  distributed  in  a  lateral,  dorsal,  and  mesial  direc- 
tion, the  two  former  groups  ending  in  the  anterior  and  lateral  col- 
umns, the  mesial  in  the  region  of  the  anterior  commissure.  Some 
of  the  mesial  dendrites  extend  beyond  the  median  line  and  form  a 
sort  of  commissure  with  the  corresponding  processes  of  the  other 
side.  The  commissural  cells  lie  principally  in  the  mesial  group  of 
the  anterior  horn,  but  occur  here  and  there  in  other  portions  of  the 
gray  substance.  Their  neuraxes  form  the  anterior  gray  commis- 
sure with  the  corresponding  processes  from  the  other  side.  After 
entering  the  white  substance  of  the  other  side,  these  neuraxes 
undergo  a  T-shaped  division,  one  branch  passing  upward  and  the 
other  downward.  The  column  cells  are  small  multipolar  elements, 
represented  by  the  cells  of  the  lateral  horns,  although  they  are 
also  found  throughout  the  entire  gray  mass.  Their  neuraxes  pass 
directly  into  the  anterior,  lateral,  and  posterior  horns. 

The  cells  of  the  column  of  Clark,  or  nucleus  doi'salis,  are  of  two 
kinds — those  in  which  the  neuraxes  pass  to  the  anterior  commis- 
sure (commissural  cells)  and  those  in  which  the  neuraxes  pass  into 
the  direct  cerebellar  tract  of  the  same  side.  The  plurifunicular 
cells  are  cells  the  neuraxes  of  which  divide  two  or  three  times  in 
the  gray  substance,  the  branches  then  passing  to  different  columns 
of  the  white  matter  on  the  same  or  opposite  side  of  the  cord.  In 
the  latter  case  the  branches  must  necessarily  extend  through  the 
commissure.  The  cells  of  the  substantia  gclatinosa  (Rolando)  are 
cells  with  short,  freely  branching  neuraxes,  which  end  after  a  short 
course  in  the  gray  mass  (Golgi's  cells).  The  posterior  horn  con-" 
tains  marginal  cells,  spindle-shaped  cells,  and  stellate  cells.  The 
first  are  situated  superficially  near  the  extremity  of  the  posterior 
horn,  their  neuraxes  extending  for  some  distance  through  the  gela- 
tinous substance  of  Rolando  and  then  into  the  lateral  column.  The 
spindle-shaped  cells  are  the  smallest  in  the  spinal  cord  and  possess  a 
rich  arborization  of  dendrites  extending  to  the  nerve-root  of  the  pos- 


THE    SPINAL    CORD. 


409 


terior  horn.  Their  neuraxes,  which  originate  either  from  the  cell- 
body  or  from  a  dendrite,  pass  over  into  the  posterior  column.  The 
stellate  cells  are  supplied  with  dendrites,  which  either  branch  in 
the  substance  of  Rolando  or  extend  into  the  column  of  Burdach. 

The  gray  matter  contains,  further,  numerous  medullated  nerve- 
fibers,  in  part  the  neuraxes  of  the  nerve-cells  previously  mentioned, 
and  in  part  collateral  and  terminal  branches  of  the  nerve-fibers  of 
the  white  matter  with  their  telodendria ;  also  supporting  cells, 
known  as  neurogliar  cells  (to  be  discussed  later),  and  blood-vessels! 

The  white  matter  of  the  spinal  cord  consists  of  medullated  fibers, 
which  are  devoid  of  a  neurilemma,  of  neurogliar  tissue,  and  of  fibrous 
connective  tissue. 

In  each  half  of  the  cord  the  white  substance,  which  surrounds 
the  gray,  is  separated  by  the  gray  matter  and  its  nerve-roots  into 


Posterior    horn 
cell. 

Crossed  pyram- 
idal column. 

Golgi     cell     of 

posterior  horn. 

Direct    cerebel- 
lar column. 
Column  cells. 

Golgi'scommis- 
sural  cells. 


Go  wars' 
column. 
Motor  cells. 


Collaterals 
of  crossed 
pyramidal 
column. 


Collaterals 
ending  in 
the  gray 
matter. 


Direct  pyramidal  column. 

Fig.  328.— Schematic  diagram  of  the  spinal  cord  in  cross-section  after  von  Lenhos- 
sek,  showing  in  the  left  half  the  cells  of  the  gray  matter,  in  the  right  half  the  collateral 
branches  ending  in  the  gray  matter. 


three  main  divisions  or  columns:  The  first  division,  lying  between 
the  anterior  median  fissure  and  the  anterior  horn,  is  the  anterior 
column ;  the  second,  lying  between  the  anterior  and  posterior 
horns,  is  the  lateral  column  (since  the  anterior  and  lateral 
columns  belong  genetically  to  each  other,  the  term  anterolat- 
eral column  is  often  used)  ;  and  the  third,  lying  between  the  poste- 
rior nerve-root  and  the  posterior  median  septum,  is  the  posterior 
column. 

By  means  of  certain  methods  it  has  been  possible  to  separate 
the  white  substance  into  still  smaller  divisions,  the  most  important 
of  which  may  here  be  described. 

In  each  anterior  column  is  found  a  narrow  median  zone  extend- 
ing along  the  entire  length  of  the  anterior  median  fissure  and  con- 


4IO 


THE    CENTRAL    NERVOUS    SYSTEM. 


THE    SPINAL    CORD.  4I  I 

taining  nerve-fibers  which  come  from  the  pyramids  of  the  medulla. 
The  majority  of  the  pyramidal  fibers  cross  from  one  side  of  the  cord 
to  the  other  in  the  lower  portion  of  the  medulla,  at  the  crossing  of 
the  pyramids,  and  form  a  large  bundle  of  nerve-fibers  found  in  each 
lateral  column,  which  will  receive  attention  later.  Some  of  the 
pyramidal  fibers  descend  into  the  cord  on  the  same  side,  to  cross  to 
the  opposite  side  at  different  levels  in  the  cord.  These  latter  fibers 
constitute  the  narrow  median  zone,  on  each  side  of  the  anterior 
median  fissure  previously  mentioned,  forming  the  anterior  or  direct 
pyramidal  tract,  or  the  column  of  Türck.  Between  the  direct 
pyramidal  tract  and  the  anterior  horn  lies  the  anterior  ground 
bundle. 

In  the  lateral  columns  are  found  a  number  of  secondary  col- 
umns, which  may  now  be  mentioned.  In  front  of  and  by  the  side 
of  the  posterior  horn  in  each  lateral  column  lies  a  large  group  of 
nerve-fibers,  forming  a  bundle  which  varies  somewhat  in  size  and 
shape  in  the  several  regions  of  the  spinal  cord,  but  which  has  in 
general  an  irregularly  oval  outline.  These  nerve-fibers  are  the 
pyramidal  fibers,  previously  mentioned,  which  in  the  lower  part  of 
the  medulla  cross  from  one  side  to  the  other,  and  for  this  reason 
are  known  as  the  crossed  pyramidal  fibers,  forming  the  crossed 
pyramidal  columns.  External  to  these  columns  and  to  the  poste- 
rior horns,  and  extending  from  the  posterior  horns  half-way  around 
the  periphery  of  the  lateral  columns,  lie  the  direct  cerebellar  col- 
umns, consisting  of  the  neuraxes  of  the  cells  of  the  columns  of 
Clark,  which  have  an  ascending  course.  Lying  just  external  to  and 
between  the  anterior  and  posterior  horns  is  a  somewhat  irregular 
zone,  the  mixed  lateral  column,  containing  several  short  bundles 
of  fibers,  the  anterior  of  which  ar^  probably  motor  ;  the  posterior, 
sensory.  In  the  ventrolateral  portions  of  the  lateral  columns, 
between  the  mixed  lateral  and  the  direct  cerebellar  columns  and 
extending  as  far  backward  as  the  crossed  pyramidal  columns,  lie 
two  not  well-defined  columns,  known  as  the  ascending  anterolat- 
eral or  Gowers's  columns  and  the  descending  anterolateral  col- 
umns ;   the  former  are  nearer  the  outer  portion  of  the  cord. 

In  the  posterior  column  Ave  distinguish  a  median  and  a  lateral 
column.  The  former  lies  along  the  posterior  median  septum,  and 
may  even  be  distinguished  externally  by  an  indentation  ;  its  upper 
portion  tapers  into  the  fascicubis  gracilis.  This  is  the  column  of 
GoU,  and  it  contains  ascending  or  centripetal  fibers.  The  lateral 
tract  lies  between  the  column  of  Goll  and  the  posterior  horn,  and 
is  known  as  the  column  of  Burdach,  posterior  ground-bundle,  or 
posterolateral  column.  It  contains  principally  the  shorter  tracts,  or 
bundles  of  longitudinal  fibers  connecting  the  adjacent  parts  of  the 
spinal  cord  with  one  another. 

Many  of  the  nerve-fibers  of  the  posterior  column  are  the  neu- 
raxes of  spinal  ganglion  cells  which  enter  the  spinal  cord  through 
the  posterior  roots.     The  cell-bodies  of  the  spinal  ganglion  or  sen- 


412  THE    CENTRAL    NERVOUS    SYSTEM. 

sory  neurones  are  situated  in  the  spinal  ganglia  found  on  the  pos- 
terior roots  of  the  spinal  nerves.  In  the  embryo  they  are  distinctly 
bipolar,  but  during  further  development  their  two  processes  approach 
each  other,  and  then  fuse  for  a  certain  distance,  forming  finally 
single  processes  which  branch  like  the  letter  T.  In  reahty,  then, 
there  are  two  processes  which  are  fused  for  a  certain  distance  from 
the  cell-body  of  each  neurone.  The  peripherally  directed  process 
is  regarded  as  the  dendrite  of  the  cell,  and  the  proximal  as  the 
neuraxis  passing  to  the  spinal  cord.  The  neuraxes  enter  the  spinal 
cord  through  the  posterior  roots  and  pass  to  the  posterior  columns, 
where  they  divide,  Y-shaped,  into  ascending  and  much  shorter 
descending  branches,  from  each  of  which  numerous  collateral 
branches  are  given  off. 

From  the  preceding  account  of  the  white  matter  of  the  spinal 
cord,  it  may  be  seen  that  it  consists  of  longitudinally  directed  neu- 
raxes arranged  in  so-called  short  and  long  tracts  or  columns.  The 
neuraxes  constituting  the  former,  after  a  short  course  through  the 
gray  matter,  emerge  from  it,  and  after  giving  off  various  collaterals, 
again  penetrate  into  the  gray  matter,  where  their  telodendria  enter 
into  contact  with  the  ganglion  cells.  The  long  columns  consist  of 
the  neuraxes  of  neurones  the  cell-bodies  of  which  are  situated  in 
the  cerebrum  or  cerebellum,  and  of  neurones  the  cell-bodies  of  which 
are  in  the  spinal  cord  or  spinal  ganglia  and  the  neuraxes  of  which 
terminate  in  the  medulla  or  cerebellum.  The  nerve -fibers  of  the 
various  columns  give  off  numerous  collaterals  which  enter  the  gray 
matter  to  end  in  telodendria.  The  collaterals  of  the  posterior  col- 
umns end  :  (i)  between  the  cells  of  the  gelatinous  substance  of  the 
posterior  horns  ;  (2)  in  the  columns  of  Clark  ;  (3)  in  the  anterior 
horns,  these  constituting  the  principal  portion  of  the  so-called  reflex 
bundles  ;  (4)  in  the  posterior  horn  of  the  opposite  side.  The  col- 
laterals of  the  lateral  columns  pass  horizontally  toward  the  central 
canal,  some  ending  in  the  anterior  horn,  others  closely  arranged 
near  the  columns  of  Clark,  and  some  arching  around  the  central 
canal,  forming  with  the  corresponding  fibers  of  the  other  side  the 
anterior  bundles  of  the  posterior  commissure.  The  collaterals  of 
the  anterior  columns  form  well-marked  plexuses  in  the  anterior 
horns  of  the  same  and  opposite  sides. 

We  have  still  to  describe  the  two  commissures.  The  anterior 
consists  of:  first,  neuraxes  from  the  commissural  cells;  second, 
dendrites  from  the  lateral  group  of  the  anterior  horn  cells  ;  and, 
third,  the  collaterals  of  the  anterolateral  column,  which  end  in  the 
gray  substance  of  the  other  side  of  the  cord.  The  posterior  com- 
missure is  probably  composed  of  the  collaterals  from  all  the  remain- 
ing columns.  The  posterior  bundle  of  this  commissure  comes 
from  the  posterior  column  ;  the  middle,  from  the  posterior  portion 
of  the  lateral  column  ;  and  the  anterior,  or  least  developed,  from 
the  anterior  portion  of  the  lateral  column,  possibly  also  from  the 
anterior  column. 


THE  CEREBELLAR  CORTEX. 


413 


In  the  gray  commissure^,  nearer  its  anterior  border,  is  situated 
the  central  canal  of  the  spinal  cord,  continuous  above  with  the 
ventricular  cavity  of  the  medulla  and  terminating  caudally  in  the 
filum  terminale.  This  canal  is  not  patent  in  the  majority  of  adults, 
being  occluded  from  place  to  place.  The  canal  is  lined  by  a  layer 
of  columnar  cells,  developed  from  columnar  cells,  known  as  spongio- 
blasts, lining  the  relatively  larger  canal  of  the  embryonic  spinal 
cord.  In  young  individuals  these  cells  are  ciliated  and  their  basal 
portions  terminate  in  long,  slender  processes  in  which  are  embedded 
neuroglia  fibers. 


B.  THE  CEREBELLAR  CORTEX, 

In  the  cerebellar  cortex  we  distinguish  three  general  layers — 
the  outer  molecular,  the  middle  granular  (rust-colored  layer),  and 
the  inner  medullary  tract. 


Blood-vessel,-- if 


*    \      /.      i    .        \ .  l — Dendrite. 


\  •'.  ''1  y  X  i  '{'i 


•  • 


~  Purkinje's  cell. 


«• 


o  ^   <- Nen'e-fiber  layer. 

^-"  -  ""  >-  ^ 

Fig.  330. — Section  through  the  human  cerebellar  cortex  vertical  to  the  surface  of  the  con- 
volution.    Treatment  with  Müller' s  fluid  ;  X  i^S- 


The   molecular  layer   contains    three  varieties   of  nerve-cells, 
those  of  Purkinje,  which  border  upon  the  granular  layer,  the  stel- 


THE  CEREBELLAR  CORTEX. 


415 


late  cells,  and  the  small  cortical  cells.  The  cells  of  Purkinje  pos- 
sess a  large  flask-shaped  body  (about  60  //  in  diameter),  from  which 
one  or  more  well-developed  dendrites  pass  toward  the  periphery. 
The  latter  branch  freely  and  the  main  arborization  has  in  each  case 
the  general  shape  of  .a  pair  of  deer's  antlers.  These  dendrites 
extend  nearly  to  the  periphery  of  the  cerebellar  cortex.  In  a 
section  horizontal  to  the  surface  of  the  organ  the  dendrites  of  the 
Purkinje's  cells  are  seen  to  lie  in  a  plane  very  nearly  vertical  to  the 
surface  of  the  convolutions,  so  that  a  longitudinal  section  through 
the  latter  would  show  a  profile  view  of  the  cells.  In  other  words, 
they  have  an  appearance  much  like  that  of  a  vine  trained  upon  a 
trellis.     The  neuraxes  of  the  cells  of  Purkinje  arise  from  their  basal 


Dendrite. 


Cell-body. 


Neuraxis. 


—  Neuraxis. 


Fig.  332. — Cell  of  Purkinje  from  the  human  cerebel- 
lar cortex.       Chrome-silver  method  ;  X  ^20. 


Claw-like    telo- 
dendrion  of 
dendrite. 


Fig.  333. — Granular  cell 
from  the  granular  layer  of  the  hu- 
man cerebellar  cortex.  Chrome- 
silver  method  ;   X  i°°- 


(inner)  ends  and  extend  through  the  granular  layer  into  the  medul- 
lary substance.  During  their  course  they  give  off  a  few  collaterals, 
which  pass  backward  to  the  molecular  layer  and  end  in  telodendria 
near  the  bodies  of  the  cells  of  Purkinje.  The  stellate  cells  lie  in 
various  planes  of  the  molecular  layer.  Their  peculiar  interest  lies 
in  the  character  of  their  neuraxes.  The  latter  are  situated  in  the 
same  plane  as  the  dendrites  of  the  cells  of  Purkinje,  run  parallel  to 
the  surface  of  the  convolution,  and  possess  two  types  of  collaterals. 
Those  of  the  first  are  short  and  branched  ;  those  of  the  second 
branch  at  a  level  with  the  cells  of  Purkinje,  and  form,  together 
with  their  telodendria,  basket-like  nets  around  the  bodies  of  these 
cells.      The   small   cortical   cells  of  the  molecular  layer  are  found 


4l6  THE    CENTRAL    NERVOUS    SYSTEM. 

in  all  parts  of  this  layer,  but  are  more  numerous  in  its  peripheral 
portion.  They  are  multipolar  cells  with  neuraxes  which  are  not 
readily  stained  and  concerning  the  fate  of  which  little  is  known. 

The  granular  layer  contains  two  varieties  of  ganglion  ele- 
ments, the  so-called  granular  cells  (small  ganglion  cells)  and  the 
large  stellate  cells.  The  dendrites  of  the  granular  cells  are  short, 
few  in  number  (from  three  to  six),  branch  but  slightly,  and  end  in 
short,  claw-like  telodendria.  Their  neuraxes  ascend  vertically  to 
the  surface  and  reach  the  molecular  layer.  At  various  points  some 
of  them  are  seen  to  undergo  a  T-shaped  division,  the  two  branches 
then  running  parallel  to  the  surface  of  the  cerebellum  in  a  plane 
vertical  to  that  of  the  dendrites  of  the  cells  of  Purkinje.  Large 
numbers  of  these  T-shaped  neuraxes  produce  the  striation  of  the 
molecular  layer  of  the  cerebellum.  It  is  very  probable  that  during 
their  course  these  parallel  fibers  come  in  contact  with  the  dendrites 
of  the  cells  of  Purkinje.  The  large  stellate  cells  are  fewer  in 
number  and  lie  close  to  the  molecular  layer,  some  of  them  even 
within  this  layer.  Their  dendrites  branch  in  all  directions,  but 
extend  principally  into  the  molecular  layer.  Their  short  neuraxes 
give  off  numerous  collaterals  which  end  in  telodendria  among  the 
granular  cells. 

The  medullary  substance  is  composed  of  the  centrifugal  neu- 
raxes of  the  cells  of  Purkinje  and  of  two  types  of  centripetal  neu- 
raxes, the  mossy  and  the  climbing  fibers.  The  position  of  their 
corresponding  nerve-cells  is  not  definitely  known.  The  mossy 
fibers  branch  in  the  granular  layer  into  numerous  twigs,  and  are 
not  uniform  in  diameter,  but  are  provided  at  different  points  with 
typical  nodular  swellings.  These  fibers  do  not  extend  beyond  the 
granular  layer.  The  climbing  fibers  pass  horizontally  through  the 
granular  layer,  giving  off  in  their  course  numbers  of  collaterals, 
which  extend  to  the  cells  of  Purkinje,  up  the  dendrites  of  which 
they  seem  to  climb. 

In  the  medullary  portion  of  the  cerebellum  are  found  a  number 
of  groups  of  ganglion  cells  known  as  central  gray  nuclei.  The 
nerve-cells  of  these  nuclei  are  multipolar,  with  numerous,  oft- 
branching"  dendrites  and  a  singfle  neuraxis. 


C  THE  CEREBRAL  CORTEX» 

The  cell-bodies  of  the  neurones  of  the  cerebrum  are  grouped  in 
a  thin  layer  of  gray  matter,  varying  in  thickness  from  2  to  4  mm., 
— which,  as  a  continuous  sheet,  completely  covers  the  white  matter 
of  the  hemispheres, — and  in  larger  and  smaller  masses  of  gray  mat- 
ter, known  as  basal  nuclei.  In  our  account  of  the  histologic  struc- 
ture of  the  cerebral  hemispheres  we  shall  confine  ourselves  in  the 
main  to  a  consideration  of  the  cerebral  cortex,  the  thin  layer  of 
gray  matter  investing  the  white  matter. 


THE  CEREBRAL  CORTEX.  41/ 

From  without  inward  the  following  layers  may  be  differentiated 
in  the  cerebral  cortex  :  (i)  a  molecular  layer  ;  (2)  a  layer  of  small 
pyramidal  cells  ;  (3)  a  layer  of  large  pyramidal  cells  ;  (4)  a  layer 
of  polymorphous  cells  ;  and  (5)  medullary  substance  or  underlying 
nerve-fibers. 

Aside  from  neurogliar  tissue,  we  find  in  the  molecular  layer  a 
large  number  of  nerve-fibers,  which  cross  one  another  in  all  direc- 
tions, but,  as  a  whole,  have  a  direction  parallel  with  the  surface  of 
the  brain.  Within  this  layer  there  are  found  :  (i)  the  tuft-like  telo- 
dendria  of  the  chief  dendritic  processes  of  the  pyramidal  cells  ;  (2) 
the  terminations  of  the  ascending  neuraxes,  arising  mostly  from  the 
polymorphous  cells  ;  and  (3)  autochthonous  fibers — i.  e.,  those  which 
arise  from  the  cells  of  the  molecular  layer  and  terminate  in  this 
layer.  The  cells  of  the  molecular  layer  may  be  classed  in  three 
general  types — polygonal  cells,  spindle-shaped  cells,  and  triangular 
or  stellate  cells.  The  polygonal  cells  have  from  four  to  six  den- 
drites, which  branch  out  into  the  molecular  layer  and  may  even 
penetrate  into  the  underlying  layer  of  small  pyramidal  cells.  Their 
neuraxes  originate  either  from  the  bodies  of  the  cells  or  from  one 
of  their  dendrites,  and  take  a  horizontal  or  an  oblique  direction, 
giving  off  in  their  course  a  large  number  of  branching  collaterals, 
which  terminate  in  knob-like  thickenings.  The  spindle=shaped 
cells  give  off  from  their  long  pointed  ends  dendrites  which  extend 
for  some  distance  parallel  with  the  surface  of  the  brain.  These 
branch,  their  offshoots  leaving  them  at  nearly  right  angles,  the 
majority  passing  upward,  assuming  as  they  go  the  characteristics 
of  neuraxes  having  collaterals.  The  arborization  is  entirely  within 
the  molecular  layer.  The  triangular  or  stellate  cells  are  similar 
to  those  just  described,  but  possess  not  two,  but  three,  dendrites. 
The  triangular  and  spindle-shaped  cells,  with  their  numerous  den- 
dritic processes  resembling  neuraxes,  are  characteristic  of  the  cere- 
bral cortex. 

The  elements  which  are  peculiar  to  the  second  and  third  layers 
of  the  cerebral  cortex  are  the  small  (about  10  //  in  diameter)  and 
large  pyramidal  cells  (from  20  p.\.o  ^o  p.  in  diameter).  They  are 
composed  of  a  triangular  body,  the  base  of  the  triangle  being  down- 
ward and  parallel  to  the  surface  of  the  brain,  of  a  chief,  principal,  or 
primordial  dendrite  ascending  toward  the  brain-surface,  of  several 
basilar  dendrites  arising  from  the  basal  surface  of  the  cell-body,  and 
of  a  neuraxis  which  passes  toward  the  medullary  substance  and 
which  has  its  origin  either  from  the  base  of  the  cell  or  from  one  of 
the  basilar  dendrites.  The  ascending  or  chief  dendrite  gives  off  a 
number  of  lateral  offshoots  which  branch  freely  and  end  in  terminal 
filaments.  The  main  stem  of  the  dendrite  extends  upward  to  the 
molecular  layer,  in  which  its  final  branches  spread  out  in  the  form 
of  a  tuft.  The  neuraxis,  during  its  course  to  the  white  substance, 
gives  off  in  the  gray  substance  from  six  to  twelve  collaterals,  which 
divide  two  or  three  times  before  terminating. 
27 


4i8 


THE    CENTRAL    NERVOUS    SYSTEM, 


Aside  from  the  fact  that  the  layer  of  polymorphous  cells  con- 
tains a  few  large  pyramidal  cells,  it  consists  principally  of  (i)  mul- 
tipolar cells  with  short  neuraxes  (Golgi's  cells)  and  (2)  of  cells  with 


Fig.  334. ^^Portions  of  vertical  section  of  human  cerebral  cortex,  treated  by  the  Golgi 

method ;  X  7°-  The  figure  shows  the  arrangement  of  the  different  cells  of  the  cerebral 
cortex  : ' gP,  Layer  of  large  pyramidal  cells ;  kP,  layer  of  small  pyramidal  cells  ;  pZ,  layer 
ofpolymOTphous  cells  (Sobotta,  "Atlas  and  Epitome  of  Histology"). 


only  slightly  branched  dendrites  and  with  neuraxes  passing  toward 
the  surface  of  the  brain  (Martinotti's  cells).  Both  these  types  of  cells 
are,  however,  not  found  exclusively  in  the  layer  of  polymorphous 


THE  CEREBRAL  CORTEX.  4I9 

cells,  but  may  be  met  with  here  and  there  in  the  layers  of  the  small 
and  large  pyramidal  cells.  The  dendrites  of  the  cells  of  Qolgi  are 
projected  in  all  directions,  those  in  the  neighborhood  of  the  medul- 
lary substance  even  penetrating  into  this  layer.  The  neuraxes 
break  up  into  numerous  collaterals,  the  telodendria  of  which  lie  ad- 
jacent to  the  neighboring  ganglion  cells.  The  cells  of  Martinotti, 
which,  as  we  have  seen,  occur  also  in  the  second  and  third  layers, 
are  either  triangular  or  spindle-shaped.  The  neuraxis  of  each  cell 
originates  either  from  the  cell-body  or  from  one  of  its  dendrites,  and 


Brush-like  telodendrion. 


Main  dendrite.  •  -  x ' 


Secondary  dendrite.  ... 


Basal  dendrite. 


Neura.xis  with  collaterals. 


^^S-    335- — Large   pyramidal    cell    from    the   human   cerebral    cortex.      Chrome-silver 

method  ;   X  I5°- 


ascends  (giving  off  collaterals)  to  the  molecular  layer,  in  which  it 
finally  divides  into  two  or  three  main  branches  ending  in  telo- 
dendria. Occasionally  it  divides  in  a  similar  manner  in  the  layer 
of  small  pyramidal  cells. 

In  the  medullary  substance  the  following  four  classes  of  fibers 
are  recognized  :  (i)  The  projection  fibers  (centrifugal) — t.  c,  those 
which  indirectly  connect  the  elements  of  the  cerebral  cortex  with  the 
periphery  of  the  body  ;  their  course  may  or  may  not  be  interrupted 


420 


THE    CENTRAL    NERVOUS    SYSTEM. 


n 


«-C 


JR.  -^  i*  '^-^     «^^  j^>  *^  "r  -^"A. 


-#-^ 


during  their  passage  through  the  basal  nuclei ;  (2)  the  commissural 

fibers,  which,  according  to 
the  original  definition,  pass 
through  the  corpus  callo- 
sum  and  anterior  commis- 
sure, thus  joining  corre- 
sponding parts  of  the  two 
hemispheres  ;  (3)  the  asso= 
ciation  fibers,  which  con- 
nect different  parts  of  the 
gray  substance  of  the  same 
hemispheres ;  and  (4)  the 
centripetal  or  terminal 
fibers  —  i.  e.,  the  terminal 
arborizations  of  those  neu- 
raxes,  the  cells  of  which 
lie  in  some  other  region  of 
the  same  or  opposite  hemi- 
sphere, or  even  in  some 
more  distant  portion  of  the 
nervous  system.  The  pro- 
jection fibers  originate  from 
the  pyramidal  cells,  some 
of  them  perhaps  from  the 
polymorphous  cells.  The 
commissural  fibers  are  also 
derived  from  the  pyramidal 
cells,  and  lie  somewhat 
deeper  in  the  white  sub- 
stance than  the  association 
fibers.  With  the  exception 
of  those  which  join  the 
anterior  commissure,  all  the 
the    corpus  callosum.     They 


Fig.  336. — Schematic  diagram  of  the  cerebral 
cortex  :  a.  Molecular  layer  with  superficial  (tan- 
gential) fibers  ;  b,  striation  of  Bechtereff-Kaes  ;  c, 
layer  of  small  pyramidal  cells  ;  d,  stripe  of  Bail- 
larger;  e,  radial  bundles  of  the  medullary  sub- 
stance ;  f,  layer  of  polymorphous  cells. 


cunei  and  those  which  lie  in  the 
commissural  fibers  are  situated  in 
give  off  during  their  passage  through  the  hemispheres  large  num 
bers  of  collaterals,  which  penetrate  at  various  points  into  the  gray 
substance  and  end  there  in  terminal  filaments.  In  this  respect 
their  arborization  is  contrary  to  the  old  definition  of  these  fibers,  and 
the  latter  must  be  completed  by  the  statement  that,  besides  joining 
symmetric  points  of  the  two  hemispheres,  they  also,  by  means  of 
their  collaterals,  may  connect  other  areas  of  the  gray  substance 
with  the  peripheral  regions  supplied  by  their  end-tufts  (Ramon  y 
Cajal,  93).  The  association  fibers  have  their  origin  also  in  the 
pyramidal  cells.  In  the  medullary  substance  their  neu  raxes  divide 
T-shaped,  and  after  a  longer  or  shorter  course  penetrate  into  the 
gray  substance  of  the  same  hemisphere,  where  they  end  as  ter- 
minal fibers.     A  few  collaterals  are,   however,  previously  given  off. 


THE    OLFACTORY    BULB.  42  1 

which  also  terminate  in  the  same  manner  in  the  gray  substance. 
The  association  fibers  form  the  bulk  of  the  medullary  rays. 

On  examining-  a  vertical  section  through  one  of  the  cerebral 
convolutions  a  number  of  successive  striations  may  be  seen.  These 
are  more  or  less  distinct,  according  to  the  region,  and  consist  of 
strands  of  medullated  nerve-fibers  between  the  layers  of  cells,  and 
parallel  with  the  surface  of  the  convolution.  The  most  superficial 
form  a  layer  of  tangential  fibers.  Between  the  molecular  layer  and 
the  layer  of  small  pyramidal  cells  is  the  striation  of  Bechtereff  and 
Kaes,  and  in  the  region  of  the  large  pyramidal  cells  the  striation  of 
Baillarger  (Gennari)  corresponding  to  the  striation  of  Vicq  d'Azyr 
in  the  cuneus.  In  figure  336  the  medullary  substance  is  seen 
below,  with  rays,  composed  of  parallel  bundles  of  fibers,  passing 
upward  into  the  gray  substance  ;  in  reality  these  fibers  penetrate 
much  higher  than  is  shown  in  the  illustration. 


D.  THE  OLFACTORY  BULB. 

The  olfactory  bulb  is  composed  of  five  layers,  which  are  espe- 
cially Avell  marked  on  its  ventral  side  :  first,  the  layer  of  peripheral 
nerve-fibers  ;  second,  the  layer  of  olfactory  glomeruli ;  third,  the 
stratum  gelatinosum,  or  molecular  layer  ;  fourth,  the  layer  of  pyr- 
amidal cells  (mitral  cells)  ;  and,  fifth,  the  granular  layer  with  the 
deeper  nerve-fibers. 

The  layer  of  peripheral  fibers  is  composed  of  the  nerve- 
bundles  of  the  olfactory  nerve  which  cross  one  another  in  various 
directions  and  form  a  nerve-plexus.  The  glomerular  layer  con- 
tains peculiar,  regularly  arranged,  round  or  oval,  and  sharply  defined 
structures,  which  were  first  accurately  studied  by  Golgi.  They  are 
known  as  glomeruli  (from  100  ju  to  300  ,m  in  diameter),  and  are  in 
reality  complexes  of  intertwining  telodendria.  As  we  shall  see, 
the  epithelial  cells  of  the  olfactory  region  of  the  nose  must  be 
regarded  as  peripheral  ganglion  cells  and  their  centripetal  (basal) 
processes  as  neuraxes.  The  telodendria  of  these  neuraxes,  together 
.with  those  of  the  dendrites  from  the  mitral  or  other  cells,  come  in 
contact  with  each  other  within  the  olfactory  glomeruli.  The  molec- 
ular layer  consists  of  small,  spindle-shaped  ganglion  cells.  Their 
neuraxes  enter  the  fifth  layer  and  their  short  dendrites  end  in  ter- 
minal ramifications  in  the  glomeruli.  The  mitral  cells  give  off 
neuraxes  from  their  dorsal  surfaces  which  also  enter  the  granular 
layer,  but  the  majority  of  their  dendrites  break  up  into  terminal 
ramifications  in  the  olfactor}-  glomeruli,  as  just  described.  The 
granular  layer  (absent  in  the  illustration)  is  made  up  of  nerve-cells 
and  nerve-fibers  ;  but,  aside  from  these,  we  find  also  large  numbers 
of  peculiar  cells  with  a  long  peripherally  and  several  short  centrally 
directed    dendrites.      No  neuraxes   can  be   demonstrated   in   these 


422 


THE    CENTRAL    NERVOUS    SYSTEM. 


cells  (granular  cells).  This  layer  also  contains  the  stellate  ganglion 
cells.  The  latter  are  not  numerous,  but  lie  scattered,  and  each  pos- 
sesses several  short  dendrites  and  a  peripherally  directed  neuraxis 
which  ends  in  the  molecular  layer  in  a  rich  arborization.  The  deep 
nerve-fibers  are  grouped  into  bundles  which  inclose  between  them 
the  granular  and  stellate  cells  just  mentioned.     These  nerve-fibers 


Mitral  cells. 


!  Large 
nerve- 
cell. 
Small 
nerve- 
cell. 


Layer  of  olfactory  ^ 
glomeruli. 


Peripheral  nerve-, 
fibers. 


Fig.  337- 


-The  olfactory  bulb,  after  Golgi  and  Ramon  y  Cajal. 
not  show^n. 


The  granular  layer  is 


are  derived  partly  fi-om  the  neuraxes  of  the  pyramidal  or  mitral  cells 
and  partly  from  the  cells  of  the  molecular  layer,  while  some  of 
them  are  centripetal  fibers  from  the  periphery,  which  end  between 
the  granules  of  the  fifth  layer. 


E.  EPIPHYSIS  AND  HYPOPHYSIS, 

In  mammalia  the  epiphysis,  or  pineal  gland,  consists  of  a 
fibrous  capsule  derived  from  the  pia  mater,  from  which  numerous 
fibrous  tissue  septa  and  processes  pass  into  the  gland,  uniting  to 
form  quite  regular  round  or  oval  compartments  in  which  closed 
follicles  or  alveoli,  whose  walls  consist  of  epithelial  cells,  are  found. 
In  the  lower  portion  of  the  epiphysis  there  is  found  a  relatively  large 
amount  of  neuroglia  tissue,  consisting  of  coarse  fibers,  as  has  been 
shown  by  Weigert.  The  epithelial  cells  forming  the  walls  of  the 
follicles  are  of  cubic  or  short  columnar- shape,  and  may  be  arranged 
in  a  single  layer  or  may  be  pseudostratified  or  stratified.      Follicles 


EPIPHYSIS    AND    HYPOPHYSIS.  423 

completely  filled  with  cellular  elements  are  found.  Other  follicles 
contain  peculiar  concretions,  known  as  brain-sand  or  acervulus,  of 
irregular  round  or  oval  or  mulberry  shape.  Medullated  nerve-fibers 
have  been  traced  into  the  epiphysis,  but  their  mode  of  termination  is 
not  known. 

The  hypophysis,  or  pituitary  body,  consists  of  two  lobes.  The 
posterior  or  infundibular  lobe  is  developed  from  the  floor  of  the  first 
primary  brain-vesicle,  and  remains  attached  to  the  floor  of  the  third 
ventricle  by  a  stalk,  known  as  the  infundibulum  ;  the  anterior  or 
glandular  lobe  develops  from  a  hollow  protrusion  derived  from  the 
primary  oral  ectoderm.  The  distal  end  of  this  protrusion  or  pouch 
comes  in  contact  with  the  anterior  surface  of  the  lower  portion  of  the 
infundibulum,  and  becomes  loosely  attached  to  it.  As  the  bones  at 
the  base  of  the  skull  develop,  the  attenuated  oral  end  of  this  pouch 
atrophies,  the  distal  end  becoming  finally  completely  severed  from 
the  buccal  cavity. 

In  the  infundibular  lobe  of  the  hypophysis  of  the  dog,  Berkley 
(94)  described  three  portions  presenting  different  microscopic  struc- 
ture. His  account  will  here  be  followed  :  (i)  An  outer  stratum 
consisting  of  three  or  four  layers  of  cells  resembling  ependymal 
cells,  which  are  separated  into  -groups  by  thin  strands  of  fibrous 
tissue  entering  from  the  fibrous  covering  of  this  lobe.  (2)  A  zone 
consisting  of  glandular  epithelial  cells  which  in  certain  places  are 
arranged  in  the  form  of  alveoli,  often  containing  a  colloid  substance. 
This  zone  merges  into  the  central  portion,  (3),  containing  variously 
shaped  cells  and  connective-tissue  partitions  with  blood-vessels.  In 
this  portion  neurogliar  cells  (see  these)  and  nerve-cells  were  stained 
by  the  chrome-silver  method. 

The  glandular  or  anterior  lobe  resembles  slightly  in  structure 
the  parathyroid.  This  lobe  is  surrounded  by  a  fibrous  tissue  capsule 
and  within  it  are  found  .variously  shaped  alveoli  or  follicles,  or, 
again,  columns  or  trabeculae  of  cells  separated  by  a  very  vascular 
connective  tissue.  In  the  alveoli  or  columns  of  cells  are  found  two 
varieties  of  glandular  cells,  which  may  be  differentiated  more  by 
their  staining  reaction  than  by  their  size  and  structure,  although 
they  present  slight  structural  differences.  One  variety  of  cells  pos- 
sesses a  protoplasm  which  shows  affinity  for  acid  stains  ;  these  are 
known  as  chromophilic  cells.  They  are  of  nearly  round  or  oval 
shape,  with  nuclei  centrally  placed,  and  have  a  protoplasm  present- 
ing coarse  granules.  The  other  variety  of  cells,  known  as  chief 
cells,  are  more  numerous  than  the  chromophilic.  They  are  of  cubic 
or  short  columnar  shape,  with  nuclei  placed  in  the  basal  portions 
of  the  cells  and  with  protoplasm  showing  a  fine  granulation  and 
with  an  affinity  for  basic  stains.  Now  and  then  alveoli  containing 
a  colloid  substance,  similar  to  that  found  in  the  alveoli  of  the  thy- 
roid gland,  may  be  observed.  The  blood-vessels  of  the  glandular 
portion  are  relatively  large,  the  majority  of  them  having  only  an 
endothelial  linine  which  comes  in  contact  with  the  glandular  cells. 


424  THE    CENTRAL    NERVOUS    SYSTEM. 

The  circulation  of  the  hypophysis  must  be  regarded  as  sinusoidal. 
In  the  glandular  portion  of  the  hypophysis  of  the  dog,  Berkley  (94) 
found  small  varicose  nerve-fibers  belonging  to  the  sympathetic  sys- 
tem. From  the  larger  bundles,  which  follow  the  blood-vessels,  are 
given  off  single  fibers,  or  small  bundles  of  such,  which  end  on  the 
glandular  elements  in  numerous  small  nodules. 


R  GANGLIA* 

In  the  course  of  peripheral  nerves  are  found  numerous  larger  and 
smaller  groups  of  nerve-cells,  known  as  ganglia.  The  neurones  of 
these  ganglia  are  in  intimate  relation  with  the  neurones  of  the  cen- 


Fig.  338. — Longitudinal  section  of  spinal  ganglion  of  cat. 

tral  nervous  system,  and  may,  therefore,  be  discussed  with  the  lat- 
ter. According  to  the  structure  and  function  of  their  neurones,  the 
ganglia  are  divided  into  two  groups — (i)  spinal  or  sensory  ganglia 
and  (2)  sympathetic  ganglia. 

The  spinal  ganglia  are  situated  on  the  posterior  roots  of  the 
spinal  nerves.  Certain  cranial  ganglia — namely,  the  Gasserian, 
geniculate,  and  auditory  ganglia,  the  jugular  and  petrosal  gan- 
glia of  the  glossopharyngeal  nerves,  and  the  root  and  trunk  ganglia 
of  the  vagi — are  classed  with  the  spinal  ganglia,  since  they  present 
the  same  structure.  The  spinal  and  sensory  cranial  ganglia  are 
surrounded  by  firm  connective-tissue  capsules,  continuous  with  the 
perineural  sheaths  of  the  incoming  and  outgoing  nerve-roots.   From 


GANGLIA.  425 

these  capsules  connective-tissue  septa  and  trabeculjE  pass  into 
the  interior  of  the  gangHa,  giving  support  to  the  nerve-elements. 
The  cell-bodies  (ganglion  cells)  of  the  neurones  constituting  these 
ganglia  are  arranged  in  layers  under  the  capsule  and  in  rows  and 
groups  or  clusters  between  the  nerv^e-fibers  in  the  interior  of  the 
ganglia.  More  recent  investigations  have  shown  that  several  types 
of  neurones  are  to  be  found  in  the  spinal  and  cranial  sensory  gan- 
glia ;  of  these,  we  may  mention  the  following:  (i)  Large  and 
small  unipolar  cells  with  T-  or  Y-shaped  division  of  the  process. 
These  neurones,  which  constitute  the  greater  number  of  all  the 
neurones  of  the  ganglia  under  discussion,  consist  of  a  round  or 
oval  cell-body,  from  which  arises  by  means  of  an  implantation  cone 


Fig.  339- — Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit ;  stained  in  methylene- 

blue  [intra  vitani). 

a  single  process,  which,  soon  after  it  leaves  the  cell,  becomes  in- 
vested with  a  medullary  sheath  and  usually  makes  a  variable  num- 
ber of  spiral  turns  near  the  cell-body.  According  to  Dogiel,  this 
process  divides  into  two  branches,  usualh'  at  the  second  or  third 
node  of  Ranvier,  sometimes  not  until  the  seventh  node  is  reached. 
Of  these  two  branches,  the  peripheral  is  the  larger,  and  enters  a 
peripheral  nerve-trunk  as  a  medullated  sensory  nerve-fiber,  termi- 
nating in  one  of  the  peripheral  sensor}-  nerve-endings  previously 
described.  The  central  process,  the  smaller  of  the  two,  becomes  a 
medullated  nerve-fiber,  which  enters  the  spinal  cord  or  medulla  in  a 
manner  described  in  a  former  section.  The  cell-body  of  each  of 
these  neurones  is  surrounded  by  a  nucleated  capsule,  continuous  with 


426 


THE    CENTRAL    NERVOUS    SYSTEM. 


the  neurilemma  of  the  single  process.  (2)  Type  II  spinal  ganglion 
cell  of  Dogiel.  Dogiel  has  recently  described  a  second  type  of  spinal 
ganglion  cell  which  differs  materially  from  the  type  just  described. 
The  cell-bodies  of  these  neurones  resemble  closely  those  of  the  typ- 
ical spinal  ganglion  neurones.  Their  single  meduUated  processes 
divide,  however,  soon  after  leaving  the  cells  into  branches  which 
divide  further  and  which  do  not  pass  beyond  the  bounds  of  the  gan- 
glia but  terminate,  after  losing  their  medullary  sheaths,  in  compli- 
cated pericapsular  and  pericellular  end-plexuses  surrounding  the 
capsules  and  cell-bodies  of  the  typical  spinal  ganglion  cells.  (3)  Mul- 
tipolar ganglion  cells  ;  in  nearly  all  spinal  and  cranial  ganglia  there 
are  found  a  few  multipolar  nerve-cells,  which  in  shape  and  struc- 
ture resemble  the  nerve-cells  of  the  sympathetic  system. 


Fig.  340. — Diagram  showing  the  relations  of  the  neurones  of  a  spinal  ganglion ; 
p.  r.,  posterior  root;  a.  r.,  anterior  root;  /.  s.,  posterior  branch  and  a.  s.,  anterior 
branch  of  spinal  nerve  ;  w.  n,  white  ramus  communicans  ;  a,  large,  and  b,  small  spinal 
ganglion  cells  with  T-shaped  division  of  process  ;  c,  type  II  spinal  ganglion  cells  (Dogiel); 
s,  multipolar  cell ;  d,  nerve-fiber  from  sympathetic  ganglion  terminating  in  pericellular 
plexuses  (slightly  modified  from  diagram  given  by  Dogiel). 


.  Entering  the  spinal  ganglia  from  the  periphery  are  found  a  rel- 
atively sinall  number  of  small,  medullated  or  nonmeduUated  nerve- 
fibers,  probably  derived  from  sympathetic  ganglia.  These  nerve- 
fibers,  medullated  and  nonmeduUated,  the  former  losing  their 
medullary  sheaths  within  the  ganglia,  approach  a  spinal  ganglion 
cell,  and  after  making  a  few  spiral  turns  about  its  process,  termi- 
nate in  pericapsular  and  pericellular  end-plexuses.  Dogiel  believes 
that  the  cell-bodies  and  capsules  thus  surrounded  by  the  terminal 
branches  of  the  sympathetic  fibers  terminating  in  the  spinal  ganglia 
belong  to  the  spinal  ganglion  cells  of  the  second  type  first  described 
by  him.  In  figure  340  is  represented  by  way  of  diagram  the 
structure  of  a  spinal  ganglion. 

In  the  medium-sized  cells  (from  30  //  to  45  [j.  in  diameter)  of  the 


GANGLIA. 


427 


spinal  ganglia  of  the  frog,  von  Lenhossek  (95)  found  centrosomes 
surrounded  by  a  clear  substance  (centrospheres).  The  entire  struc- 
ture lay  in  a  depression  of  the  nucleus  and  contained  more  than 
twelve  extremely  minute  granules  (centrosomes),  which  showed  a 
staining  reaction  different  from  that  of  the  numerous  concentrically 
laminated  granules  present  in  the  protoplasm.  This  observation  is 
interesting  in  that  it  proves  that  centrosome  and  sphere  occur  also 
in  the  protoplasm  of  cells  which  have  not  for  a  long  time  under- 
gone division  and  in  which  there  is  no  prospect  of  future  division. 

Sympathetic  Ganglia. — The  ganglia  of  the  sympathetic  ner- 
vous system  comprise  those  of  the  two  great  ganglionated  cords, 
found  on  each  side  of  the  vertebral  column  and  extending  from  its 
cephalic  to  its  caudal  end,  with  which  may  be  grouped  certain  cranial 
ganglia  having  the  same  structure, — namely,  the  sphenopalatine, 
otic,  ciliary,  sublingual,  and  submaxillary  ganglia  ;  also  three  un- 


Fig.  341.— Neurone  from  inferior  cervical  sympathetic  ganglion  of  a  rabbit;  methylene- 

blue  stain. 


paired  aggregations  of  ganglia,  found  in  front  of  the  spinal  column, 
of  which  the  cardiac  is  in  the  thorax,  the  semilunar  in  the  abdomen, 
and  the  hypogastric  in  the  pelvis  ;  and  further,  large  numbers  of 
smaller  ganglia,  the  greater  number  of  which  are  of  microscopic 
size  and  are  found  in  the  walls  of  the  intestinal  canal  and  bladder, 
in  the  respiratory  passages,  in  the  heart,  and  in  or  near  the  majority 
of  the  glands  of  the  body. 

The  sympathetic  ganglia  are  inclosed  in  fibrous  tissue  capsules 
continuous  with  the  perineural  sheaths  of  their  nerve-roots.  The 
thickness  of  the  capsule  bears  relation  to  the  size  of  the  ganglion, 
being  thicker  in  the  larger  and  thinner  in  the  smaller  ones.  From 
these  capsules  thin  connective-tissue  septa  or  processes  pass  into 
the  interior  of  the  ganglia,  supporting  the  nerve  elements. 

The  sympathetic  neurones,  the  cell-bodies  and  dendritic  processes 
of  which  are  grouped  to  form  the  sympathetic  ganglia,  are  variously 


428 


THE    CENTRAL    NERVOUS    SYSTEM. 


shaped  unipolar,  bipolar,  and  multipolar  cells,  the  cell-bodies  of 
which  are  surrounded  by  nucleated  capsules,  continuous  with  the 
neurilemma  of  their  neuraxes.  In  the  sympathetic  ganglia  of  mam- 
malia and  birds  the  great  majority  of  sympathetic  neurones  are 
multipolar,  although  in  nearly  all  ganglia  a  small  number  of  bipolar 
and  unipolar  cells  are  to  be  found,  usually  near  the  poles  of  the 
ganglia. 

The  dendrites  of  the  sympathetic  neurones  in  any  one  ganglion 
branch  repeatedly.  Of  these  branches,  some  extend  to  the  per- 
iphery of  the  ganglion,  where  they  interlace  to  form  a  peripheral 
subcapsular  plexus,  while  others  interlace  to  form  plexuses  between 
the  cell-bodies  of  the  neurones  in  the  interior  of  the  ganglion — 
pericellular  plexuses.  These  pericellular  plexuses  are  external  to 
the  capsules  surrounding  the  cell -bodies  of  the  sympathetic  neurones. 


Fig.  342. — From  section  of  semilunar  ganglion  of  cat ;  stained  in  methylene-blue,  intra 
vitam  (Huber,  Journal  of  Mo7'phology,  1899). 

The  neuraxes  of  the  sympathetic  neurones,  the  majority  of 
which  are  nonmedullated,  the  remainder  surrounded  by  delicate 
medullary  sheaths,  arise  from  the  cell-bodies  either  from  implanta- 
tion cones  or  from  dendrites  at  variable  distances  from  the  cell- 
bodies,  leave  the  ganglion  by  way  of  one  of  its  nerve-roots,  and 
terminate  in  heart  muscle  tissue,  nonstriated  muscle,  and  glandular 
tissue,  and  to  some  extent  in  other  ganglia,  both  sympathetic  and 
spinal.  Terminating  in  all  sympathetic  ganglia  are  found  certain 
small  medullated  nerve-fibers,  varying  in  size  from  about  1.5  //  to 
3  //.  The  researches  of  Gaskell,  Langley,  and  Sherrington  have 
shown  that  these  small  medullated  nerve-fibers  leave  the  spinal 
cord  through  the  anterior  roots  of  the  spinal  nerves  from  the  first 
dorsal  to  the  third   or  fourth  lumbar  and   reach  the  sympathetic 


GANGLIA. 


429 


ganglia  through  the  zvhite  rami  comnmnica^ites.  Similar  small 
meduUated  nerve-fibers  are  found  in  certain  cranial  nerves.  These 
small  meduUated  nerve-fibers,  which  may  be  spoken  of  as  %vhite 
rami  fibers,  after  a  longer  or  shorter  course,  in  which  they  may 
pass  through  one  or  several  ganglia  without  making  special  con- 
nection with  the  neurones  contained  therein,  terminate  in  some 
sympathetic  ganglion  in  a  very  characteristic  manner.  After  enter- 
ing the  sympathetic  ganglion  in  which  they  terminate,  they  branch 
repeatedly  while  yet  meduUated.  The  resulting  branches  then  lose 
their  medullary  sheaths  and  divide  into  numerous  small,  varicose 
nerve -fibers,  which  interlace  to  form  intracapsular  plexuses,  which 
surround  the  cell-bodies  of  the  sympathetic  neurones.  In  the 
sympathetic   gangha  of   mammalia  such  intracapsular  pericellular 


Fig   343.— From  section  of  stellate  ganglion  of  dog,  stained  in  methylene^blue  and  alum 
carmin  :  a,  white  ramus  fiber  (Huber,  Journal  of  Morphology,  1899). 

plexuses  may  be  very  simple,  consisting  of  only  a  few  varicose 
nerve-fibers,  or  very  complicated,  consisting  of  many  such  fibers. 
In  the  sympathetic  ganglia  of  reptilia,  in  which  are  found  very 
large  sympathetic  neurones,  the  white  rami  fibers  are  wound  spirally 
about  the  cell-bodies  of  such  neurones  before  terminating  in  com- 
plicated pericellular  plexuses.  In  the  frog  and  other  amphibia  the 
sympathetic  neurones  are  unipolar  nerve-cells.  The  white  rami 
fibers  terminating  in  the  sympathetic  ganglia  of  amphibia  are  wound 
spirally  about  the  single  processes  of  these  unipolar  cells  while  yet 
meduUated  fibers,  but  they  lose  their  medullary  sheaths  before  ter- 
minating in  the  intracapsular  pericellular  plexuses.  From  what 
has  been  said  concerning  the  white  rami  fibers  and  their  relation  to 
the  sympathetic  neurones,  it  is  evident  that  the  sympathetic  neu- 


430 


THE    CENTRAL    NERVOUS    SYSTEM. 


rones,  the  cell-bodies  and  dendrites  of  which  are  grouped  to  form 
the  sympathetic  ganglia,  form  terminal  links  in  nerve  or  neurone 
chains  ;  the  second  link  of  these  chains  is  formed  by  neurones  the 
cell-bodies  of  which  are  situated  in  the  spinal  cord  or  medulla,  the 


Fig.  344. — From  section  of  sympathetic  ganglion  of  turtle,  showing  white  rami 
fibers  wound  spirally  about  a  large  process  of  a  unipolar  cell,  and  ending  in  pericellular 
plexus  {Yi.Mhtx,  Journal  of  Morphology,  1899). 

neuraxes  leaving  the  cerebrospinal  axis  through  the  white  rami  as 
small  medullated  nerve-fibers,  which  terminate  in  pericellular  plex- 
uses inclosing  the  cell-bodies  of  the  sympathetic  neurones. 

Large  medullated  nerve -fibers,  the  dendrites  of  spinal  ganglion 
neurones,  reach  the  sympathetic  ganglia  through  the  white  rami. 


Fig.  345. — From  section  of  sympathetic  ganglion  of  frog,  showing  spiral  fiber  (white  ramus 
fiber)  and  pericellular  plexus  (Ylviher,  Journal  0/ Morphology,  1899). 


They  make,  however,  no  connection  with  the  sympathetic  neurones, 
but  pass  through  the  ganglia  to  reach  the  viscera,  where  they  ter- 
minate in  special  sensoiy  nerve-endings  or  in  free  sensory  nerve- 
endings. 


RELATIONSHIP    OF    NEURONES. 


431 


G.  GENERAL   SURVEY  OF  THE  RELATIONS   OF 
NEURONES  TO  ONE  ANOTHER  IN  THE 
CENTRAL  NERVOUS  SYSTEM. 


THE 


The  following  figures  illustrate  the  modern  theories  with  re- 
gard to  the  relationship  of  the  neurones  in  a  sensorimotor  reflex 
cycle.  The  pathway  along  which  the  impulse  from  the  stimulated 
area  of  the  body  is  transmitted  to  the  motor  nerve  end-organ  tra- 
verses two  neurones  (primary  neurones)  which  are  in  contact  by 
means  of  their  telodendria  situated  within  the  gray  matter  of  the 
spinal  cord.  The  cell-body  of  the  sensory  neurone  lies  within  the 
spinal  ganglion  ;  that  of  the  motor  neurone,  in  the  anterior  horn  of 
the  spinal  cord.     The  dendrite  of  the  sensory  neurone  commences 


mN 


Fig.  346. — Schematic  diagram  of  a  sensorimotor  reflex  arc  according  to  the  modern 
neurone  theory  ;  transverse  section  of  spinal  cord  :  wyV,  Motor  neurone  ;  sA^,  sensory 
neurone  ;  C^,  nerve-cell  of  the  motor  neurone  ;  C^,  nerve-cell  of  the  sensory  neurone  ; 
d,  dendrite  ;  n,  neuraxis  of  both  neurones ;  t,  telodendria  ;  M,  muscle-fiber ;  h,  skin 
with  peripheral  telodendrion  of  sensory  neurone. 


as  a  telodendrion  in  the  skin  or  perhaps  also  in  more  deeply  seated 
structures,  and  transmits  a  cellulipetal  impulse,  while  its  cellulifugal 
neuraxis  and  telodendrion  (the  latter  in  the  gray  matter  of  the  cord) 
transfer  the  impulse  to  the  cellulipetal  telodendrion  of  the  motor 
neurone.  The  cellulifugal  neuraxis  of  the  latter  finally  ends  as  a 
telodendrion  in  the  muscle.      (Figs.  346  and  347.) 

In  the  case  of  longer  tracts  the  conditions  are  somewhat  more 
complicated,  as,  for  instance,  in  tracing  the  impulse  along  the  sen- 
sory fibers  to  the  cortex  of  the  brain,  and  from  there  along  the 
motor  fibers  to  the  responding  muscle.  In  such  cases  secondary 
neurones  are  called  into  play  by  means  of  their  telodendria,  which 
are  necessarily  in  contact  with  the  primary  neurones  just  described. 


432 


THE    CENTRAL    NERVOUS    SYSTEM. 


When  we  take  into  consideration  the  simplest  possible  case,  that 
of  the  motor  segment  of  such  a  neurone-chain,  we  find,  for  instance 
(Fig.  348),  that  the  neuraxis  of  a  pyramidal  cell  in  the  brain  cortex 
(psychic  cell)  enters  the  white  substance  and  traverses  it  as  a  nerve- 
fiber  through  the  peduncle  and  the  pyramid  into  the  crossed 
pyramidal  tract  of  the  opposite  side.  Here  its  telodendria  come  in 
contact  with  those  of  the  motor  neurone  of  the  anterior  horn. 

In  the  foregoing  instance  the  motor  nerve  tract  is  composed  of 
two  neurones — of  a  motor  neurone  of  the  first  order,  extending 
from  the  cortex  of  the  brain  to  the  anterior  cornua  of  the  spinal 
cord,  and  of  a  motor  neurone  of  the  second  order,  the  elements 
of  which  extend  from  the  anterior  cornua  to  the  telodendria  in  the 
muscle. 


ci  -■ 


Fig.  347. — Schematic  diagram  of  a  sensorimotor  reflex  cycle ;  sagittal  section  of 
the  spinal  cord:  C^,  Motor  cells  of  the  anterior  cornua;  n,n,  neuraxes  ;  sA^,  sensory 
neurone  ;  C-,  spinal  ganglion  cell ;  C,  collaterals  of  the  sensory  neuraxes  ;  d,  dendrite  of 
sensory  neurone ;  the  broken  lines  at  the  cells  on  the  left  indicate  their  dendrites. 


The  sensory  tract  may  likewise  be  composed  of  neurones  of  the 
first  and  second  orders.  The  cellulifugal  neuraxis  arising  from  a 
cell  of  the  spinal  ganglion  passes  to  the  posterior  column  of  the 
cord,  gives  off  collaterals  to  the  latter,  and  then  passes  upward  by 
means  of  its  ascending  branch  through  the  posterior  column  to  the 
medulla.  Although  here  the  relationship  is  not  so  clearly  defined 
as  in  the  motor  tract,  it  may  nevertheless  be  assumed  that  the  cellu- 
lifugal (but  centripetally  conducting)  neuraxis  at  some  point  or 
other  terminates  in  telodendria  (sensory  neurone  of  the  first  order), 
which  enter  into  contact  with  the  corresponding  structures  of  a  cell 
of  the  spinal  cord  or  medulla  oblongata.      These  cells  would  then 


RELATIONSHIP    OF    NEURONES. 


433 


constitute  the  sensory  neurones  of  the  second  order.  Exactly  how 
their  cellulifugal  neuraxes  end  has  not  as  yet  been  fully  determined, 
but  it  is  very  probable  that  in  this  case  the  telodendria  are  repre- 
sented by  the  coarse  end-fibers  which  penetrate  into  the  brain  cor- 
tex, and  here  seem  to  come  in  contact  with  the  dendrites  of  the  pyr- 
amidal cells. 


^^sN^ 


—  iiVi 


Fig.  348,— Schematic  diagram  of  the  reflex  tracts  between  a  peripheral  organ  and 
the  brain  cortex  :  H,  Cerebral  cortex  ;  mN^,  motor  neurone  of  the  first,  sN~,  sensory 
neurone  of  the  second,  degree  ;  C  S  motor  cell  of  the  spinal  cord  ;  C^,  sensory  cell  of  a 
spinal  ganglion;  C^,  pyramidal  cell  of  the  brain  cortex  (pyschic  cell)  ;  C^,  nerve-cell 
of  a  sensory  neurone  of  the  second  degree  ;  n,  n,  n,  n,  neuraxes  ;  J,  d,  dendrites  ;  c,  c,  c,  c, 
collaterals  ;  t,  t,  telodendria;  sN^,  sensory  neurone  first  degree;  mN'^,  motor  neurone 
second  degree. 

28 


434 


THE    CENTRAL    NERVOUS    SYSTEM. 


R  THE  NEUROGLIA, 

The  neuroglia  tissue  is  an  especially  differentiated  supporting 
tissue  found  in  the  central  nervous  system,  the  optic  chiasm,  optic 
nerve  and  retina  and  for  some  distance,  at  least,  in  the  olfactory 
nerve.  Its  relation  to  other  tissues  has  long  been  a  matter  of  con- 
troversy, but  modern  observers  have  shown  quite  conclusively  that 
neuroglia  tissue  is  of  ectodermal  origin.  It  should  not  be  under- 
stood, however,  that  the  neuroglia  tissue  forms  the  only  supporting 
tissue  of  the  central  nervous  system.  In  all  parts  of  the  central 
nervous  system,  more  especially,  however,  in  the  spinal  cord,  there 
is  found  true  connective  tissue  of  mesoblastic  origin,  more  especially 
in  connection  with  the  blood-vessels. 

At  an  early  stage  of  embryonic  development  there  are  seen  in 
the  spinal  cord,  and  also  in  the  brain,  elements  radially  disposed 
around  the  neural  canal,  which  upon  closer  observation  appear 
to  be  processes  emanating  from  the  epithelial  cells  lining  the  neural 
canal.  These  processes  may  undergo  repeated  dichotomous  divi- 
sion, ending  finally  in  a  swelling 
near  the  periphery  of  the  cord. 
These  cells  are  known  as  epen- 
dymal  cells,  and  are  differenti- 
ated from  ectodermal  cells,  called 
spongioblasts.  In  later  stages 
the  radial  arrangement  is  still 
preserved,  but  the  cell-bodies  no 
longer  all  border  upon  the  cen- 
tral canal,  many  being  found  at 
varying  distances  from  the  latter. 
At  this  stage  in  the  development 
of  the  spinal  cord,  the  elements 
retaining  their  original  charac- 
teristics are  situated  only  in  the 
region  of  the  ventral  and  dorsal 
fissures  of  the  spinal  cord,  and 
during  further  development  in- 
crease in  number. 

These  observations  would 
seem  to  indicate  that  at  least  a 
portion  of  the  neurogliar  cells,  which  develop  from  the  ependymal 
cells  previously  mentioned,  originate  from  the  epithelium  of  the 
central  canal,  and  that  from  here  they  are  gradually  pushed  toward 
the  periphery  of  the  cord.  This  assumption  is  still  further  strength- 
ened by  the  fact  that  later  the  epithelial  cells  of  the  central  canal 
still  continue  to  divide.  Later  observations  (Schaper,  97)  show,  how- 
ever, that  neurogliar  cells  develop  also  from  certain  undifferentiated 
germinal   cells   of  the  neural   canal,   of   ectodermal   origin,   which 


Fig.  349. — Neurogliar  cells  :  a.  From 
spinal  cord  of  embryo  cat  ;  b,  from  brain  of 
adult  cat :  stained  in  chrome-silver. 


THE    NEUROGLIA.  435 

wander  from  their  position  near  the  neural  canal  toward  the  per- 
iphery of  the  medullary  tube,  where  they  develop  into  neuroglia 
cells. 

Owing  to  the  fact  that  of  the  several  methods  now  at  hand  for 
studying  neuroglia  tissue  no  two  give  identical  results,  the  views 
concerning  this  tissue  are  still  at  variance.  The  Golgi  or  chrome- 
silver  method  was  for  many  years  the  only  method  by  means  of 
which  the  elements  of  neuroglia  tissue  were  brought  to  light  with 
any  degree  of  clearness.  In  preparations  of  the  central  nervous 
system  treated  with  this  method  all  the  neuroglia  elements  appear 
as  cells  with  processes.  The  cell  bodies  of  these  cells  as  also  the 
processes  being  stained  black  or  nearly  black  (as  seen  with  trans- 
mitted light)  so  that  the  relations  of  the  processes  to  the  cellular 
constituents  can  not  be  ascertained,  investigators  who  have  made  use 
of  this  method  in  their  study  of  neuroglia  distinguish  two  essentially 
different  cellular  elements  of  the  neuroglia:  ependymal  cells,  pre- 
viously mentioned,  and  neuroglia  cells,  so-called  spider  cells  or 
astrocytes.  The  astrocytes  are  grouped  under  two  main  heads : 
short-rayed  astrocytes,  possessing  a  few  short  processes,  found  in  the 
gray  matter,  and  long-rayed  astrocytes  with  many  fine  and  long  pro- 
cesses, which  do  not  appear  to  branch,  found  both  in  the  gray  and 
white  matter.  The  two  types  of  astrocytes  are  not  clearly  defined, 
as  intermediate  types  are  also  found.  In  figure  349  are  shown  two 
astrocytes  (long-rayed)  as  seen  in  chrome-silver  preparations. 

A  number  of  investigators  have  in  recent  years  perfected  methods 
by  means  of  which  neuroglia  tissue  could  be  stained  differentially — 
Weigert,  Mallory,  Benda.  In  tissues  treated  after  any  one  of  these 
rather  complicated  differential  staining  methods  the  processes  of  the 
neuroglia  cells  as  seen  in  chrome-silver  preparations  appear  in  the 
form  of  well-contoured  fibrils,  which  are  not  interrupted  by  the  cell- 
bodies  of  the  neuroglia  cells,  from  which  they  are.  either  entirely 
separated  or  are  seen  to  pass  through  the  protoplasm  ot  the  cells 
without  losing  their  identity.  In  preparations  of  the  central  nervous 
system  stained  after  Benda's  differential  neuroglia  tissue  staining 
method,  numerous  neuroglia  cells  may  be  observed  both  in  the  gray 
and  white  matter.  Certain  of  these  cells  possess  very  little  proto- 
plasm, others — and  these  are  in  the  majorit}^ — present  it  to  an  ap- 
preciable extent.  The  shape  of  such  cells  varies.  When  situated 
in  the  main  mass  of  the  white  matter  of  the  spinal  cord,  and  seen  in 
cross-sections  of  the  cord,  they  present  an  irregular  triangular  and 
quadrangular  form,  with  protoplasmic  branches  which  arise  from  the 
angles  and  which  extend  for  a  variable  distance  between  the  nerve- 
fibers.  In  such  preparations  it  may  be  seen  that  the  neuroglia 
fibers  pass  in  close  proximity  to  the  neuroglia  cells,  apparently  em- 
bedded in  the  outermost  part  of  their  protoplasm,  and  often  follow- 
ing the  protoplasmic  processes.  This  view  of  the  structure  of  neu- 
rogliar  tissue  is  more  in  accord  with  recent  investigations  on  this 


436 


THE    CENTRAL    NERVOUS    SYSTEM. 


subject  (Weigert,  Mallory,  Benda,  Krause,  Hardesty,  Ruber).  In 
figure  350  are  shown  two  neuroglia  cells  from  a  cross-section  of  a 
human  spinal  cord,  in  which  the  relation  of  neuroglia  fibers  to  neu- 
roglia cells  is  shown. 


Fig.  350. — Typical  neuroglia  cells,  from  cross-section  of  the  white  matter  of  the 
human  spinal  cord,  stained  after  Benda' s  selective  neuroglia  tissue  staining  method; 
X  1200  (Huber,  "Studies  on  Neuroglia  Tissue,"   Vaughan  Festschri/i,  1903). 


L  THE  MEMBRANES   OF   THE   CENTRAL 
NERVOUS  SYSTEM, 

The  membranes  of  the  central  nervous  system  (meninges)  are 
three  in  number:  the  outer,  or  dura  mater ;  the  middle,  or  arach- 
noid; and  the  inner,  ox  pia  mater. 

Around  the  brain  the  dura  mater  is  very  intimately  connected 
with  the  periosteum  and  presents  a  smooth  inner  surface.  It  con- 
sists of  an  inner  and  an  outer  layer,  the  two  being  separated  from 
each  other  only  in  certain  regions.  At  such  points  either  the  inner 
layer  is  pushed  inward  to  form  a  duplicature,  as  in  the  falx  cerebri 
and  falx  cerebelli,  tentorium,  and  diaphragma  sellae,  or  the  outer 
layer  is  pushed  outward  to  form  small,  blindly  ending  sacs.  The 
venous  and  lymphatic  sinuses  lie  between  the  two  layers.    The  outer 


THE    MEMBRANES    OF    THE    CENTRAL    NERVOUS    SYSTEM.  437 

layer  of  the  dura  is  continued  some  distance  along  the  cerebrospinal 

nerves. 

The  dura  mater  of  the  spinal  cord  does  not  form  the  periosteum 
for  the  bones  forming  the  vertebral  canal  ;  these  possess  their  own 
periosteum.  The  spinal  dura  mater  is  covered  on  its  outer  surface 
by  a  layer  of  endothelial  cells  and  is  separated  from  the  wall  of  the 
vertebral  canal  by  the  epidural  space,  containing  a  venous  plexus 
imbedded  in  loose  areolar  connective  tissue  and  adipose  tissue. 

The  dura  consists  chiefly  of  connective-tissue  bundles  having  a 
longitudinal  direction  along  the  spinal  cord.  Within  the  cranium, 
however,  the  bundles  of  the  inner  and  outer  layers  cross  each  other  ; 
those  of  the  outer  having  a  lateral  direction  anteriorly  and  a  mesial 
posteriorly  ;  those  of  the  inner,  a  mesial  direction  anteriorly  and  a 
lateral  posteriorly.  In  the  falx  cerebri,  tentorium,  etc.,  the  fibers  are 
arranged  radially,  extending  from  their  origin  toward  their  borders. 
The  shape  and  size  of  the  connective-tissue  cells  vary  greatly,  and 
their  processes  form  a  network  around  the  bundles  of  connective 
tissue.  Few  elastic  fibers  are  present,  and,  according  to  K.  Schultz, 
these  are  entirely  absent  in  the  new-born  ;  they  are  somewhat  more 
numerous  in  the  dura  of  the  spinal  cord.  The  dura  is  very  rich  in 
blood-capillaries,  and  the.  presence  of  lymphatic  channels  in  com- 
munication with  the  subdural  space  may  be  demonstrated  by  means 
of  puncture-injections.  The  inner  surface  of  the  dura  mater  is  cov- 
ered by  a  layer  of  endothelial  cells. 

The  dura  mater  is  quite  richly  supplied  with  nerves,  especially 
in  certain  regions.  These  are  of  two  varieties  :  ( i)  Vasomotor  fibers, 
which  form  plexuses  in  the  adventitial  coat  of  the  arteries,  and 
would  seem  to  terminate  in  the  muscular  coat  of  the  arteries  ;  (2) 
medullated  nerve-fibers,  which  either  accompany  the  blood-vessels 
in  the  form  of  larger  or  smaller  bundles  or  have  a  course  mde- 
pendent  of  the  vessels.  After  repeated  division  these  medullated 
nerve-fibers  lose  their  medullary  sheaths  and  terminate  betw^een  the 
connective-tissue  bundles  in  fine  varicose  fibrils,  which  may  often 
be  traced  for  long  distances  (Huber,  99). 

The  arachnoid  is  separated  from  the  dura  by  a  space  which  is 
regarded  as  belonging  to  the  lymphatic  system— the  subdural  space. 
The  outer  boundary  of  the  arachnoid  consists,  as  does  the  inner  lin- 
ing of  the  dura,  of  a  layer  of  flattened  endothelial  cells.  The  arach- 
noid is  made  up  of  a  feltwork  of  loosely  arranged  connective-tissue 
trabecular,  which  also  penetrate  into  the  lymph-space  between  it 
and  the  pia — the  subarachnoid  space.  For  a  short  distance  from 
their  points  of  origin  the  cerebrospinal  nerves  are  accompanied  by 
arachnoid  tissue.  In  the  brain  the  arachnoid  covers  the  convolu- 
tions and  penetrates  with  its  processes  into  the  sulci.  These  pro- 
cesses are  especially  well  developed  in  the  so-called  cisterns  ;  in 
the  cisterna  cerebellomedullaris,  fossae  Sylvii,  etc.  In  the  spinal 
cord  the  subarachnoid  space  is  separated  by  the  ligamenta  den- 
ticulata  into  two  large  communicating  spaces — a  dorsal  and  a  ven- 


438 


THE    CENTRAL    NERVOUS    SYSTEM. 


Gray 
matter. 


tral.     The  dorsal  space  is  further  divided  by  the  septum  posticum, 
best  developed  in  the  cervical  region. 

At  certain  points,  usually  along  the  superior  longitudinal  sinus, 
the  outer  surface  of  the  arachnoid  is  raised  into  villi,  Avhich  are 
covered  by  the  inner  layer  of  the  dura,  and  form  with  the  latter  the 
Pacchionian  bodies  or  granulations.  These  villi  are  connected 
with  the  arachnoid  by  pedicles  so  delicate  that  they  often  seem  to 
be  suspended  free  in  the  venous  current  of  the  sinus. 

The  subarachnoid  space  contains  numerous  blood-vessels,  some 
of  which  are  free  and  others  attached  to  the  arachnoid.  Their 
adventitia  is  covered  by  endothelium ;  hence  the  subarachnoid  space 

would  seem  to  assume 
here  the  character  of  a 
perivascular  space. 

The  trabeculae  and 
membranes  composing 
the  arachnoid  tissue  show 
a  great  similarity  to  those 
of  the  mesentery,  and  es- 
pecially to  those  of  the 
omentum.  The  whole 
constitutes  a  typical  are- 
olar connective  tissue, 
interrupted  at  numerous 
points  and  covered  by  a 
continuous  layer  of  en- 
dothelial cells.  Large 
numbers  of  spiral  fibers 
are  found  here  twining 
around  single  or  groups 
of  connective-tissue  fi- 
bers. The  arachnoid 
possesses  neither  blood- 
vessels nor  nerves. 

The  pia  mater  cov- 
ers the  entire  surface  of 
the  brain  and  spinal  cord, 
dipping  down  into  every  fissure  and  crevice.  In  the  spinal  cord  it 
consists  of  an  outer  and  an  inner  lamella,  the  former  being  com- 
posed of  bundles  of  connective  tissue  containing  elastic  fibers. 
As  a  rule,  the  course  of  the  fibers  is  longitudinal.  Externally 
this  layer  is  covered  by  a  layer  of  endothelium.  The  blood- 
vessels lie  between  the  outer  and  inner  layers  of  the  pia.  The 
inner  layer  (pia  intima)  is  made  up  of  much  finer  elements,  and 
is  covered  on  both  sides  by  endothelium.  It  is  this  layer  which 
accompanies  the  blood-vessels  penetrating  into  the  spinal  cord, 
surrounding  their  adventitia  and  forming  with  the  latter  the  limits 
of  their  perivascular  spaces.      These  are  in  com.munication  with  the 


White 
matter. 


Fig.  351. — Section  through  the  cerebral  cortex  of  a 
rabbit.     The  blood-vessels  are  injected ;  X  4°' 


BLOOD-VESSELS    OF    THE    CENTRAL    NERVOUS    SYSTEM.  439 

interpial  spaces,  and,  by  means  of  the  adventitia  of  the  blood-vessels, 
with  the  subarachnoid  space.  Aside  from  those  just  described, 
numerous  fine,  nonvascular,  connective-tissue  septa  penetrate  from 
the  pia  mater  into  the  substance  of  the  spinal  cord.  Wherever  the 
pia  mater  penetrates  the  spinal  cord,  the  latter  is  hollowed  out, 
forming  the  so-called  pial  funnels.  Just  beneath  the  pia  there  is 
found  in  the  spinal  cord  of  man  a  well-developed  layer  of  neuroglia 
fibers.  The  posterior  longitudinal  septum  of  the  spinal  cord  consists 
(in  the  thoracic  region)  exclusively  of  neurogliar  elements,  but  in  the 
cervical  and  lumbar  regions  the  pia  also  enters  into  its  peripheral 
formation. 

In  the  brain,  however,  the  conditions  are  somewhat  different. 
Here  the  external  layer  of  the  pia  disappears,  leaving  only  a  single 
layer  analogous  to  the  pia  intima  of  the  spinal  cord. 

The  pia  mater  enters  into  the  formation  of  the  choroid  plexus. 
This  structure  consists  of  numerous  freely  anastomosing  blood- 
vessels, which  form  villus-like  processes,  the  surfaces  of  which  are 
covered  by  squamous  or  cubic  epithelial  cells.  This  epithelium  is 
regarded  as  a  continuation  of  the  ventricular  epithelium,  and  is  cili- 
ated, at  least  in  embryonic  life  and  in  the  lower  classes  of  verte- 
brates. From  an  embryologic  point  of  view  the  whole  structure 
represents  the  brain-wall  reduced  to  a  single  layer  of  epithelium 
(internal  epithelial  investment)  pushed  forward  into  the  ventricle  by 
the  vessels  and  pia  mater. 

Since  the  dura  and  arachnoid  accompany  the  cerebrospinal 
nerves  for  some  distance,  it  is  obvious  that  the  lymph-vessels 
of  the  nasal  mucous  membrane  (see  these)  may  also  be  injected 
from  the  subarachnoid  space  (compare  also  Key  and  Retzius). 

The  pia  mater,  like  the  dura  mater,  receives  two  varieties  of 
nerve-fibers  :  (i)  Vasomotor  fibers,  which  form  plexuses  in  the  ad- 
ventitial coat  of  the  arteries  and  terminate  in  the  muscular  layer  of 
the  arteries.  These  may  be  traced,  to  the  small  precapillary 
branches  of  the  vessels.  (2)  Larger  and  smaller  bundles  of  rela- 
tively large,  medullated  nerve-fibers,  which  accompany  the  larger 
pial  vessels,  forming  loose  plexuses  in  or  on  the  adventitial  coat  of 
the  vessels.  After  repeated  divisions  these  medullated  nerves  lose 
their  medullary  sheaths  and  terminate  in  the  adventitia  of  the  ves- 
sels, in  long,  varicose  fibrils  or  in  groups  of  such  fibrils  (Huber, 
99)- 


J.    BLOOD-VESSELS  OF  THE  CENTRAL  NERVOUS 

SYSTEM, 

The  blood-vessels  of  the  central  nervous  system  present  certain 
peculiarities  which  deserve  special  consideration. 

The  spinal  cord  receives  its  arterial  blood  mainly  through  vessels 
which  accompany  the  spinal  nerve  roots  and  through  numerous 
anastomoses  from  a  plexus  in  the  pia  mater  in   which  there  may  be 


440  THE    CENTRAL    NERVOUS    SYSTEM. 

recognized  a  median  ventral  unpaired  line  of  anastomosis  and  along 
each  half  of  the  spinal  cord  four  other  lines  of  anastomosis.  From  the 
median  unpaired  line  of  anastomosis  some  200  to  2  50  branches  pass 
into  the  anterior  fissure,  each  of  which  generally  divides  into  a  right 
and  left  branch  just  in  front  of  the  commissure,  each  branch  being 
distributed  to  the  gray  matter  in  its  immediate  vicinity.  The  white 
matter  receives  its  blood-supply  from  vessels  of  the  plexus  in  the 
pia  mater,  from  which  numerous  fine  branches  are  given  off  which 
terminate  in  capillary  networks  and  extend  as  far  as  the  gray  matter. 
The  veins  return  the  blood  to  the  veins  of  the  pia  mater,  following 
in  the  main  the  course  of  the  arteries.  The  central  and  peripheral 
arteries  do  not  anastomose  except  through  capillaries  and  now  and 
then  precapillaries  (Adamkiewicz  and  Kadyi). 

In  the  cerebral  cortex  the  capillaries  are  particularly  numerous, 
and  are  closely  meshed  wherever  groups  of  ganglion  cells  occur. 
In  the  medullary  substance  they  are  somewhat  less  closely  arranged, 
their  meshes  being  oblong.  In  the  cerebellum  the  arrangement  is 
analogous.  Of  all  the  layers  composing  the  cerebellum  the  granu- 
lar is  the  most  vascular ;  within  it  the  capillaries  are  also  densely 
arranged  and  form  a  close  network. 

Lymphatic  vessels  with  definitive  walls  have  thus  far  not  been 
discovered  in  the  central  nervous  system.  The  blood-vessels  through 
the  central  nervous  system  are,  however,  surrounded  by  perivascular 
spaces,  which  maybe  regarded  as  performing  the  function  of  lymph- 
atic vessels. 

TECHNIC. 

The  organs  of  the  central  nervous  system  are  best  fixed  in  Müller' s 
fluid,  washed  with  water,  cut  in  celloidin,  and  stained  with  carmin.  Such 
preparations  are  suitable  for  general  topographic  work. 

Special  structures — as,  for  instance,  the  medullary  sheaths  of  the  nerve - 
fibers,  the  ganglion  cells,  the  relations  of  the  different  neurones  and  den- 
drites to  one  another,  etc. — require  different  treatment. 

The  medullary  sheath  may  be  demonstrated  as  follows  (Weigert): 
Pieces  of  tissue  (spinal  cord,  for' instance),  fixed  as  usual  in  Miiller's  or 
Erlicki's  fluid,  are  transferred  without  washing  to  alcohol,  imbedded 
in  celloidin,  and  cut.  Before  staining  the  sections  it  is  necessary  to 
subject  them  to  the  mordant  action  of  a  neutral  copper  acetate 
solution  (a  saturated  solution  of  the  salt  diluted  with  an  equal  volume 
of  water).  The  sections  may  be  subjected  to  the  mordant  action  of 
this  solution,  but  the  following  procedure  is  more  convenient :  The 
specimens,  imbedded  in  celloidin  and  fastened  to  a  cork  or  a  block 
of  wood,  are  placed  for  one  or  two  days  in  the  copper  solution  just 
described.  At  the  expiration  of  this  time  the  pieces  of  tissue  will  have 
become  dark,  and  the  surrounding  celloidin  light  green.  They  are  then 
placed  in  80^  alcohol,  in  which  they  may  be  preserved  for  any  length 
of  time.  The  sections  are  then  stained  in  the  following  solution  :  i  gm. 
of  hematoxylin  is  dissolved  in  10  c.c.  absolute  alcohol,  and  90  c.c.  of 
distilled  water  are  then  added  (the  fluid  must  remain  exposed  to  the  air 
for  a  few  days)  ;  the  addition  of  an  alkali — as,  for  instance,  a  cold  satu- 


TECHNIC.  441 

rated  solution  of  lithium  bicarbonate  (i.  c.c.  to  100  c.c.  of  hematoxylin 
solution) — brings  out  the  staining  power  of  the  solution  at  once.  In 
this  stain  the  sections  are  placed  (at  room -temperature)  for  a  day,  and 
then  in  a  thermostat  (40°  C.)  for  a  few  hours.  The  sections,  now  quite 
dark,  are  washed  in  distilled  water  and  then  placed  in  the  so-called  dif- 
ferentiating fluid.  The  latter  consists  of  borax  2  gm.,  ferrocyanid  of 
potassium  2.5  gm.,  and  distilled  water  100  gm.  In  this  fluid  the  color 
of  the  sections  is  differentiated  by  virtue  of  the  circumstance  that  the 
medullary  sheath  retains  the  dark  stain,  while  the  remaining  structures, 
such  as  the  ganglion  cells,  etc.,  are  bleached  to  a  pale  yellow.  The  time 
required  for  this  differentiation  varies,  but  it  is  usually  complete  at  the  end 
of  a  few  minutes.  The  sections  are  then  washed  in  distilled  water,  dehy- 
drated in  alcohol,  cleared  in  carbol-xylol  (carbolic  acid  i  part,  xylol  3 
parts)  and  mounted  in  balsam. 

Weigert's  new  method  is  more  complicated,  but  fruitful  of  cor- 
respondingly better  results.  The  preliminary  treatment  remains  the  same. 
After  the  tissues  have  been  imbedded  in  celloidin  and  this  hardened  in 
80^  alcohol,  they  are  transferred  to  a  mixture  composed  of  equal  parts 
of  a  cold  saturated  aqueous  solution  of  neutral  copper  acetate  and  10^ 
aqueous  solution  of  sodium  and  potassium  tartrate,  and  the  whole  is  placed 
in  the  thermostat.  Larger  pieces — as,  for  instance,  the  pons  Varolii  of 
man — may  remain  in  the  solution  longer  than  twenty-four  hours,  after 
which  time,  however,  the  mixture  must  be  changed  ;  but  in  no  case  should 
the  specimens  be  permitted  to  remain  longer  than  forty-eight  hours  in 
this  solution.  The  temperature  in  the  thermostat  should  not  be  high, 
otherwise  the  specimens  will  become  brittle.  The  objects  are  now  placed 
in  a  simple  aqueous  solution  of  neutral  copper  acetate,  either  saturated 
or  half  diluted  with  water,  and  again  put  in  the  oven.  They  are  then 
rinsed  in  distilled  water  and  placed  in  80  ^  alcohol ;  after  remaining 
in  this  for  one  hour,  they  are  in  a  condition  to  cut,  but  may  be  preserved 
still  longer  if  desired.  Cut  and  stain  in  the  customary  manner.  The 
staining  solution  is  prepared  as  follows  :  (a)  lithium  carbonate  7  c.c.  and 
distilled  water  93  c.c.  (saturated  aqueous  solution)  ;  (^^)  hematoxylin  i 
gm.,  absolute  alcohol  10  c.c.  ;  both  a  and  ^  keep  for  some  time,  and  may 
be  kept  on  hand  as  stock  solutions.  Shortly  before  using,  9  parts  of  a 
and  I  part  of  d  are  mixed.  After  remaining  in  this  solution  for  from 
four  to  five  hours  at  room-temperature  the  sections  are  well  stained,  but 
do  not  overstain  even  if  allowed  to  remain  in  the  solution  for  twenty-four 
hours.  In  the  case  of  loose  celloidin  sections  the  use  of  the  differentiat- 
ing fluid  is  superfluous.  Hence  this  method  is  particularly  advantageous 
when  the  gray  and  the  white  matter  can  not  be  distinguished  macro- 
scopically.  Finally,  the  sections  are  washed  in  water,  placed  in  95% 
alcohol,  cleared  with  carbol-xylol  or  anilin-xylol  (in  the  latter  case 
carefully  washed  with  xylol),  and  mounted  in  xylol -balsam.  The  medul- 
lated  fibers  appear  dark  blue  to  black,  the  background  pale  or  light 
pink,  and  the  celloidin  occasionally  bluish.  In  order  to  remove  the  latter 
color,  it  is  only  necessary  to  wash  the  sections  in  0.5^  acetic  acid  in- 
stead of  ordinary  water ;  a  process,  however,  not  to  be  recommended 
in  the  case  of  very  delicate  preparations — as,  for  instance,  the  cerebral 
cortex.  In  applying  Weigert's  methods  a  certain  thickness  of  section 
(not  exceeding  25  p.)  is  essential,  since  in  thicker  sections  the  medullary 
sheaths  are  not  sharply  differentiated  from  the  surrounding  tissue. 


442  THE    CENTRAL    NERVOUS    SYSTEM. 

For  thick  sections  the  modified  Weigert  method,  or  Pal's  method, 

is  employed.  After  the  specimens  have  been  treated  according  to  Wei- 
gert's  method  up  to  the  point  of  staining  with  hematoxylin,  they  are  placed 
for  from  twenty  to  thirty  minutes  in  a  0.25%  solution  of  potassium  per- 
manganate. As  differentiating  fluid  a  solution  of  oxalic  acid  i  gm., 
potassium  sulphite  i  gm.,  and  water  200  c.c.  is  used,  care  being  taken, 
as  in  the  case  of  Weigert's  differentiating  fluid,  that  the  gray  matter  is 
thoroughly  bleached  (here  entirely  colorless)  and  the  white  matter  dark. 
By  this  method  the  medullary  sheaths  are  stained  blue,  while  the  rest  of 
the  structure  remains  colorless.  The  staining  is  very  precise,  but  not  so 
intense  as  by  Weigert's  method.  Hence  its  adaptability  for  thicker 
sections. 

Benda's  method  is  a  modification  of  the  Weigert-Pal  methods.  The 
tissues  are  hardened  in  Müller' s  or  Erlicki's  fluid,  imbedded  in  celloidin, 
and  cut.  The  sections  are  then  subjected  to  the  action  of  the  following 
mordant  for  from  twelve  to  twenty-four  hours  :  liquor  ferri  ter  sulphatis 
I  part,  distilled  water  2  parts.  They  are  then  thoroughly  rinsed  in  two 
tap -waters  and  one  distilled  water  and  then  stained  in  the  following  hem- 
atoxylin solution:  hematoxylin  i  gm.,  absolute  alcohol  10  c.c,  distilled 
water  90  c.c;  in  which  they  remain  for  twenty-four  hours.  They  are 
next  washed  in  tap-water  for  from  ten  to  fifteen  minutes  and  treated  with 
a  0.25^  aqueous  solution  of  permanganate  of  potassium  until  the  gray 
and  the  white  matter  are  differentiated,  after  which  they  are  rinsed  in 
distilled  water  and  bleached  in  the  following  solution  until  the  gray  mat- 
ter has  a  light  yellow  color :  hydric  sulphite  5  to  10  parts,  distilled  water 
100  parts.  The  sections  are  then  washed  in  tap-water  for  from  one  to  two 
hours,  rinsed  in  distilled  water,  dehydrated,  cleared  in  carbol-xylol,  and 
mounted  in  balsam.  Medullary  sheaths  will  be  stained  a  bluish-black ; 
other  structures,  a  light  yellow.  Sections  stained  after  the  Weigert,  Pal, 
or  Benda  method  may  be  counterstained  in  Van  Gieson's  picric-acid- 
fuchsin  stain  (i^  aqueous  solution  of  acid  fuchsin,  15  parts;  saturated 
aqueous  solution  of  picric  acid,  50  parts ;  distilled  water,  50  parts) . 
The  fibrous  connective  tissue  in  the  sections  and  degenerated  areas  stains 
a  light  red. 

Apathy  (97)  demonstrates  the  fibrillar  elements  of  the  nervous 
system  in  invertebrates  and  vertebrates  by  means  of  his  gold  method. 
Fresh  tissue  may  be  used,  or  tissue  already  fixed.  In  the  first  case  thin 
membranes  are  placed  for  at  least  two  hours  in  a  i  '^  solution  of  yellow 
chlorid  of  gold  in  the  dark,  then  carried  over  without  washing  into  a  i  ^ 
solution  of  formic  acid  (sp.  gr.  1.223),  ^^'^  finally  exposed  for  from 
six  to  eight  hours  to  the  light  (the  formic  acid  may  have  to  be  changed). 
These  specimens  are  best  mounted  directly  in  syrup  of  acacia  or  in  con- 
centrated glycerin.  In  his  second  method  Apathy  fixes  vertebrate  tissues 
for  twenty-four  hours  in  sublimate -osmic  acid  (i  vol.  saturated  solution 
of  corrosive  sublimate  in  0.5^  sodium  chlorid  solution  combined  with  i 
vol.  1^0  osmic  acid  solution),  washes  repeatedly  in  water,  and  places  for 
twelve  hours  in  an  aqueous  iodo-iodid  of  potassium  solution  (potassium 
iodid  I  %  and  iodin  0.5%).  The  further  treatment  is  the  same  as  after  or- 
dinary corrosive  sublimate  fixation.  Finally,  the  specimens  are  imbedded 
in  paraffin  with  the  aid  of  chloroform,  cut,  and  mounted  by  the  water 
method.  The  whole  process,  up  to  the  point  of  imbedding  in  paraffin, 
is  carried  out  in  the  dark.     The  sections  are  then  passed  through  chloro- 


TECHNIC.  443 

form  and  alcohol  into  water,  where  they  are  allowed  to  remain  for  at  least 
six  hours  ;  or  they  may  be  washed  in  water,  placed  for  one  minute  in  i  ^ 
formic  acid,  again  washed  in  water,  immersed  for  twenty-four  hours  in  a 
I  ^  solution  of  gold  chlorid,  rinsed  in  water,  and  finally  placed  in  a  i  ^ 
formic  acid  solution  and  exposed  to  the  light.  For  the  latter  purpose 
glass  tubes  are  employed  in  which  the  slides  are  placed  obliquely,  with  the 
sections  downward.  A  uniform 'illumination  of  the  section  with  "as 
intense  a  light  and  low  a  temperature  "  as  possible  are  conditions  indis- 
pensable to  the  attainment  of  successful  results.  The  sections  are  then 
again  washed  in  water  and  mounted  in  glycerin  or  syrup  of  acacia,  or  in 
Canada  balsam  after  being  dehydrated.  Thin  membranes  are  stretched 
upon  small  frames  of  linden  wood  especially  prepared  for  this  purpose. 
Their  further  treatment  is  then  the  same  as  that  of  sections  fixed  to  the  slide. 
If  successful,  the  nerve-fibrils  appear  dark  violet  to  black.  The  large 
ganglia  in  the  spinal  cord  of  lophius,  the  calf,  etc.,  are  especially  recom- 
mended as  appropriate  vertebrate  material. 

Bethe  (1900)  has  recommended  the  following  method  for  staining 
neurofibrils  and  Qolgi=nets  in  the  central  nervous  system  of  vertebrates : 

The  perfectly  fresh  tissue  is  cut  in  thin  lamellse,  varying  in  thickness 
from  4  to  10  mm.  These  are  placed  on  pieces  of  filter-paper  and 
then  in  3  to  7.5%  nitric  acid,  in  which  they  remain  twenty-four  hours. 
From  the  hardening  fluid  the  pieces  of  tissue  are  transferred  into  96^ 
alcohol,  where  they  remain  for  from  twelve  to  twenty-four  hours.  They 
are  then  placed  in  a  solution  of  ammonium -alcohol, — ammonium  (sp.  gr. 
0.95  to  0.96),  I  part;  distilled  water,  3  parts  ;  96%  alcohol,  8  parts, — 
in  which  they  remain  for  from  twelve  to  twenty-four  hours.  The  temper- 
ature of  this  solution  should  not  exceed  20°  C.  The  tissues  are  then 
placed  for  from  six  to  twelve  hours  in  96%  alcohol,  and  next  in  a  hydro- 
chloric acid-alcohol  solution, — concentrated  hydrochloric  acid  (sp.  gr. 
1. 1 8 — 37%),  I  part;  distilled  water,  3  parts;  and  96^  alcohol,  8  to  12 
parts, — in  which  they  remain  for  several  hours.  The  temperature  of  this 
solution  should  not  exceed  20°  C.  The  tissues  are  then  again  placed  in 
96^  alcohol  for  from  ten  to  twenty-four  hours,  and  next  in  distilled  water 
for  from  two  to  six  hours.  The  tissues  are  now  placed  for  twenty-four 
hours  in  a  4%  aqueous  solution  of  ammonium  molybdate.  (This  solution 
should  be  kept  at  a  temperature  varying  from  10°  to  15°  C,  if  it  is  de- 
sired to  stain  the  neurofibrils  ;  or  at  a  temperature  varying  from  10°  to 
30°  C,  if  it  is  desired  to  bring  out  the  Golgi-nets. )  After  the  ammo- 
nium molybdate  treatment,  the  tissues  are  rinsed  in  distilled  water,  placed 
in  96^  alcohol  for  from  ten  to  twenty- four  hours,  then  in  absolute  alco- 
hol for  a  like  period,  cleared  in  xylol  or  toluol,  and  imbedded  in  par- 
affin. Sections  having  a  thickness  of  10  /jt  are  now  cut  and  fixed  to  slides 
with  Mayer's  albumin-glycerin.  Since  the  various  solutions  used  in  the 
fixation  and  further  treatment  of  the  tissues  do  not  act  with  the  same  in- 
tensity on  all  parts  of  the  piece  of  tissue  to  be  studied,  and  since  the  differ- 
entiation and  staining  depend  on  a  relative  proportion  (not  yet  fully  de- 
termined) of  the  mordant  (ammonium  molybdate)  and  the  stain  in  a 
given  section,  it  is  advised  by  Bethe  to  cut  large  numbers  of  sections  and 
fix  to  each  slide  about  three  sections  from  different  parts  of  the  series. 
After  fixation  of  the  sections  to  the  slide  the  paraffin  is  removed  with 
xylol ;  and  they  are  then  carried  through  absolute  alcohol  into  distilled 
water,  in  which,  however,  the  sections  remain  only  long  enough  to  re- 


444  THE    CENTRAL    NERVOUS    SYSTEM. 

move  the  alcohol.  The  slides  (with  the  sections  fixed  to  them)  are  then 
taken  from  the  water  and  rinsed  with  distilled  water  from  a  water-bottle. 
The  slide  is  then  wiped  dry  on  its  under  surface  and  edges  with  a  clean 
cloth,  and  about  i  c.c.  to  1.5  c.c.  of  distilled  water  placed  on  the  slide 
over  the  sections.  The  slides  are  now  placed  in  a  warm  oven  with  a  tem- 
perature of  55°  C.  to  60°  C.  for  a  period  of  time  varying  from  two  to 
ten  minutes.  No  definite  time  can  here  be  given  ;  sections  from  each 
block  of  tissue  need  to  be  tested  until  the  right  stay  in  the  warm  oven  is 
ascertained.  The  slides  are  then  taken  from  the  warm  oven  and  rinsed 
two  or  three  times  in  distilled  water  and  again  dried  as  previously 
directed.  They  are  then  covered  with  the  following  staining  solution 
and  again  placed  in  the  warm  oven  for  about  ten  minutes  :  toluidin-blue, 
I  part ;  distilled  water,  3000  parts.  The  stain  is  washed  off"  with  dis- 
tilled water  and  the  sections  are  placed  in  96^  alcohol  until  no  more 
stain  is  given  off — usually  for  from  three-fourths  to  two  minutes.  They 
are  then  dehydrated  in  absolute  alcohol,  passed  through  xylol  twice,  and 
mounted  in  xylol  balsam.  For  a  fuller  discussion  of  this  method  the 
reader  is  referred  to  Bethe's  account  in  "  Zeitsch.  f.  Wissensch.  Mikrosk. , ' ' 
vol.  XVII,  1900. 

For  staining  neuroglia  Weigert  (95)  has  recommended  a 
method,  from  which  we  give  the  following  :  A  solution  is  made  consisting 
of  5^  neutral  acetate  of  copper,  5^  ordinary  acetic  acid,  and  2.5^ 
chrome -alum  in  water.  The  chrome-alum  and  water  are  first  boiled 
together,  the  acetic  acid  then  added,  and  finally  the  finely  pulverized 
neutral  copper  acetate,  after  which  the  mixture  is  thoroughly  stirred  and 
allowed  to  cool.  To  this  solution  10^  formalin  may  be  added.  Objects 
not  over  0.5  cm.  in  diameter  are  placed  in  this  fluid  for  eight  days,  the 
mixture  being  changed  at  the  end  of  a  few  days.  By  this  means  the 
pieces  of  tissue  are  at  the  same  time  fixed  and  prepared  for  subsequent 
staining  by  the  action  of  the  mordant.  If  separation  of  the  two  processes 
be  desired,  the  specimens  are  fixed  for  about  four  days  in  a  10^  formalin 
solution  (which  is  changed  in  a  few  days),  and  then  placed  in  the 
chrome -alum  mixture  without  the  addition  of  formalin.  Specimens  thus 
fixed  may  be  preserved  for  years  without  disadvantage,  and  may  then  be 
subjected  to  further  treatment  by  other  methods,  Golgi's  for  instance. 
Washing  with  water,  dehydration  in  alcohol,  and  imbedding  in  celloidin 
are  the  next  steps.  The  sections  are  then  placed  for  about  ten  minutes 
in  a  0.33^  solution  of  potassium  permanganate,  washed  by  pouring  water 
over  them,  and  placed  in  the  reducing  fluid  (5%  chromogen  and  5^ 
formic  acid  of  a  specific  gravity  of  1.20;  then  filter  carefully,  and 
add  10  c.c.  of  a  10^  solution  of  sodium  sulphite  to  90  c.c.  of  the  fluid). 
The  sections,  rendered  brown  by  the  potassium  permanganate,  readily 
decolorize  in  a  few  minutes,  but  it  is  better  to  leave  them  for  from  two  to 
four  hours  in  the  solution.  If  it  be  desirable  to  decolorize  entirely  the 
connective  tissue,  no  further  steps  need  be  taken  preliminary  to  staining  ; 
if  not,  the  reducing  fluid  is  poured  off"  and  the  sections  are  rinsed  twice 
in  water  and  then  placed  in  an  ordinary  saturated  solution  of  chromogen 
(5^  chromogen  in  distilled  water,  carefully  filtered).  The  sections  are 
left  in  this  solution  overnight,  and  the  longer  they  remain  in  it,  the  more 
marked  will  be  the  contrast,  as  far  as  stain  is  concerned,  between  the  con- 
nective and  nervous  tissues ;  then  water  is  again  twice  poured  upon  the 
sections  and  they  are  ready  for  staining.     This  process  consists  in  a 


TECHNIC.  445 

modified  fibrin  stain  {ind.  Technic).  The  iodo-iodid  of  potassium  solu- 
tion is  the  same  (saturated  solution  of  iodin  in  a  5%  iodid  of  potassium 
solution).  Instead  of  the  customary  gentian -violet  solution,  a  hot  satu- 
rated alcoholic  (70%  to  80%  alcohol)  solution  of  methyl-violet  is  made, 
and,  after  cooling,  the  clear  portion  decanted  off;  to  every  100  c.c.  of 
this  fluid  5  c.c.  of  a  5^  aqueous  solution  of  oxalic  acid  is  added.  The 
staining  takes  place  in  a  very  short  time.  The  sections  are  then  rinsed 
and  normal  salt  solution  and  the  iodo-iodid  of  potassium  solution  poured 
over  them  (5%  iodid  of  potassium  solution  saturated  with  iodin),  and 
washed  off  with  water  and  dried  with  filter-paper  and  decolorized  in  the 
anilin  oil -xylol  solution  in  the  proportion  of  1:1.  The  reactions  are 
rapid,  and  the  thickness  of  the  section  should  not  exceed  20  /i.  This 
method  is  best  adapted  to  the  central  nervous  system  of  the  human  adult ; 
it  has  as  yet  not  been  sufficiently  tested  for  other  vertebrates. 

Mallory''  s  Selective  Neuroglia  Fiber-Staining  Methods. — Fix  tissues  in 
10^  formalin  four  days  ;  place  in  saturated  aqueous  solution  of  picric 
acid  four  days  ;  place  in  5  %  aqueous  solution  of  ammonium  bichromate 
four  to  six  days  in  warm  oven  at  38°  C;  dehydrate  and  imbed  in  cell- 
oidin  ;  sections  may  be  stained  in  Weigert's  fibrin  stain  and  differenti- 
ated with  equal  parts  of  anilin  oil  and  xylol,  or  they  may  be  treated  as 
follows:  Place  sections  in  0.5^  aqueous  solution  of  permanganate  of 
potassium  twenty  minutes ;  wash  in  distilled  water  one  to  three  minutes ; 
place  in  I  ^  aqueous  solution  of  oxalic  acid  thirty  minutes  ;  wash  in  dis- 
tilled water  ;  stain  in  phosphotungstic-acid-hematoxylin  solution  (hemat- 
oxylin I  g. ,  distilled  water  80  c.c,  10^  aqueous  solution  of  phosphotung- 
stic  acid  [Merk],  20  c.c,  peroxid  of  hydrogen  [U.S. P.],  2  c.c.)  for 
twelve  to  twenty-four  hours  ;  rinse  in  distilled  water  and  place  for  five  to 
twenty  minutes  in  an  alcoholic  solution  of  ferric  chlorid  (ferric  chlorid  30 
g.,  30^  alcohol  100  c.c)  ;  rinse  in  distilled  water  and  dehydrate  quickly, 
clear  in  oil  of  bergamot,  and  mount  in  xylol-balsam. 

Be /Ida's  Selective  Neuroglia  Staining  Method. — Benda  has  for  some 
years  concerned  himself  with  perfecting  selective  staining  methods  for 
differentiating  certain  constituents  of  the  protoplasm  of  cells,  and  has 
recently  published  a  number  of  staining  methods,  by  all  of  which  neuroglia 
fibers  may  be  more  or  less  successfully  differentiated.  According  to  him, 
certain  hematoxylin  solutions,  used  after  proper  fixation  and  mordanting 
of  the  tissues,  may  be  used  for  neuroglia  stains;  also  hematoxylin  staining, 
followed  by  staining  with  an  acid-anilin  water  crystal  violet  solution. 
These  will  not  be  considered  here.  We  wish,  however,  to  call  especial  atten- 
tion to  the  following  method  for  staining  neuroglia  tissue,  suggested  by 
Benda,  since  it  has  certain  advantages  not  possessed  by  other  selective  neu- 
roglia stains.  Fix  small  pieces  of  tissue  in  10%  formalin;  place  in 
Weigert's  chrome-alum  solution  (formula  given  above),  four  days  in  warm 
oven  at38°C.;  wash  in  water  twenty-four  hours;  dehydrate  in  graded 
alcohols  ;  imbed  in  paraffin  ;  cut  thin  sections  and  fix  these  to  slides  with 
the  albumin -glycerin  fixative  ;  remove  paraffin  and  place  sections  in  mor- 
dant consisting  of  a  4%  aqueous  solution  of  ferric  alum  ;  rinse  thoroughly 
in  two  tap  waters  and  one  distilled  water  ;  place  in  a  sodium  sulphaliz- 
arate  solution  (add  to  distilled  water  a  sufficient  quantity  of  a  saturated 
solution  of  sodium  sulphalizarate  in  yo^iji  alcohol  to  give  it  a  sulphur-yellow 
color)  twenty-four  hours  ;  rinse  in  distilled  water  ;  stain  for  fifteen  min- 
utes in  a  0.1%  aqueous  solution  toluidin  blue,  which  should  be  heated  after 


44^  THE    EYE. 

the  sections  are  in  the  stain  until  the  solution  steams ;  allow  the  stain  to 
cool ;  rinse  in  distilled  water  ;  wash  in  a  i  ^  aqueous  solution  of  glacial 
acetic  acid  for  a  few  seconds  or  in  acid  alcohol  (six  drops  of  hydrochloric 
acid;  70%  alcohol  100 c.c.)  for  a  few  seconds  ;  dry  sections  with  filter- 
paper  ;  dip  sections  a  few  times  in  absolute  alcohol  ;  differentiate  in  cre- 
osote, ten  minutes  to  an  hour — control  now  and  then  under  the  micro- 
scope ;  wash  in  several  xylols  and  mount  in  xylol -balsam.  Neuroglia  fibers 
blue,  chromatin  of  neuroglia  cell  nuclei  a  purplish  blue,  protoplasm  of 
neuroglia  cells  brownish  red  to  bluish  red. 


VIII.   THE    EYE. 

A.  GENERAL  STRUCTURE. 

The  organ  of  vision  consists  of  the  eyeball,  or  bulbus  oculi, 
and  the  entering  optic  nerve. 

In  the  eyeball  we  distinguish  three  tunics  :  (i)  a  dense  external 
coat,  the  tunica  fibrosa  or  externa,  which  may  be  regarded  as  a 
continuation  of  the  dura  mater,  consisting  of  an  anterior  transparent 
structure,  called  the  cornea,  and  the  remaining  portion,  known  as 
the  tunica  sclej^otica,  or,  briefly,  the  sclera ;  (2)  within  the  tunica 
fibrosa  a  vascular  tunic,  the  tunica  vasculosa  or  media,  subdivided 
into  the  choroid,  ciliary  body,  and  iris  ;  (3)  an  inner  coat,  the  tunica 
interna,  which  consists  of  two  layers,  the  inner  being  the  retina ; 
the  outer,  the  pigment  membrane.  The  latter  lines  the  internal 
surface. of  the  tunica  vasculosa  throughout.  Within  the  eyeball 
are  the  aqneotis  humor,  the  lens,  and  the  vitreous  body.  The  lens  is 
attached  to  the  ciliary  body  by  a  special  accessory  apparatus — the 
zonida  ciliaris.  These  two  structures — the  lens  and  its  fixation 
apparatus — divide  the  cavity  of  the  eyeball  into  two  principal  cham- 
bers, the  one  containing  the  aqueous  humor  and  the  other  the 
vitreous.  The  former  is  further  subdivided  by  the  iris  into  an 
anterior  and  a  posterior  chamber.  During  life  the  latter  is  only  a 
narrow  capillary  cleft. 


B.  DEVELOPMENT  OF  THE  EYE. 

In  man  the  eyes  begin  to  develop  during  the  fourth  week  of 
embryonic  life,  and  at  first  consist  of  a  pair  of  ventrolateral  diver- 
ticula, projecting  from  the  anterior  brain  vesicle.  These  evaginations 
gradually  push  outward  toward  the  ectoderm,  and  are  then  known 
as  the  primary  optic  vesicles.  The  slender  commissural  segments 
connecting  the  vesicles  with  the  developing  brain  are  termed  the 
optic  stalks. 

Very  soon  a  process  of  invagination  takes  place  ;  that  portion 
of  the  vesicular  wall  nearest  the  ectoderm  is  pushed  inward,  thus 


DEVELOPMENT    OF    THE    EYE. 


447 


forming  a  double-walled  cup — the  secondary  optic  vesicle,  ox  optic 
cup.  An  internal  and  an  external  wall  may  now  be  differentiated, 
continuous  at  the  margin  of  the  cup.  At  the  same  time  a  disc-like 
thickening  of  the  adjacent  ectoderm  sinks  inward  toward  the  mouth 
of  the  cup-shaped  optic  vesicle,  forming  the  first  trace  of  the  lens. 
During  the  development  of  the  secondary  optic  vesicle  a  groove 


Blood-vessels  Sphincter 

Vein.  Canal  of  Petit,  of  the  iris.  Cornea,  pupillae.  Iris. 


Fontana's  spaces. 


Post,  cili- 
ary arte 
ries. 
A.  cen- 
tralis ret- 
inae 


Pigment 

layer. 
„a 

-Sclera. 
'"Choroid. 


Rectus 
muscle. 

\dipose 
tissue. 


^  #<i'-"'-^ 


Physiologic  excavation. 


Macula  lutea. 


Fig.  352. —Schematic  diagram  of  the  eye  (after  Leber  and  Flamming)  :  a.  Vena  vorti- 
cosa  ;  b,  choroid  ;  /,  lens. 


is  formed  on  its  ventral  side,  extending  from  the  marginal  ring  into 
the  optic  stalk.  This  is  the  embryonic  optic  fissure,  or  the  choroi- 
dal fissure.  At  the  edges  of  the  groove  the  two  layers  of  the  optic 
cup  are  continuous.  This  groove  serves  for  the  penetration  of 
mesoblastic  tissue  and  blood-vessels  into  the  interior  of  the  optic 
cup,  and  in  its  wall  the  fibers  of  the  optic  nerve  develop. 

The  outer  layer  of  the  secondary  optic  vesicle  becomes  the//^- 
ment  membrane  ;  the  inner,  the  retina.  The  optic  nerve-fibers  con- 
sist not  only  of  the  centripetal  neuraxes  of  certain  ganglion  cells  m 
the  retina,  but  also  of  centrifugal  neuraxes,  which  pass  out  from 
the  brain  (Froriep). 

The  invaginating  ectoderm  which  later  constitutes  the  lens  is 
constricted  off  from  the  remaining  ectoderm  in  the  shape  of  a  vesi- 


448  THE    EYE, 

cle,  the  mesial  half  of  which  forms  the  lens  fibers  by  a  longitudinal 
growth  of  its  cells,  while  the  lateral  portion  forms  the  thin  anterior 
epithelial  capsule  of  the  lens.  The  epithelium  of  the  ectoderm 
external  to  the  lens  differentiates  later  into  the  external  epithelium 
of  the  cornea  and  conjunctiva,  neither  of  which  structures  is  at 
this  stage  sharply  defined  from  the  remaining  ectoderm.  It  is  only 
during  the  development  of  the  eyelids  that  a  distinct  demarcation 
is  established.  All  the  remaining  portions  of  the  eye,  as  the  vitre- 
ous body,  the  vascular  tunic  with  the  iris,  the  sclera  with  the 
substantia  propria  of  the  cornea  and  the  cells  of  Descemet's  layer, 
are  products  of  the  mesoderm. 


C  TUNICA   FIBROSA  OCULL 

J,  THE  SCLERA. 

The  sclera  is  the  dense  fibrous  tissue  covering  of  the  eyeball, 
and  is  directly  continuous  with  the  transparent  cornea.  At  the  poste- 
rior mesial  portion  of  the  eyeball,  the  sclera  is  perforated  for  the  en- 
trance of  the  optic  nerve,  this  region  being  known  as  the  lamina 
cribrosa.  The  sclera  consists  of  bundles  of  connective-tissue  fibers 
arranged  in  equatorial  and  meridional  layers.  At  the  external 
scleral  sulcus,  in  the  vicinity  of  the  cornea,  the  arrangement  of  the 
fibers  is  principally  equatorial.  The  tendons  of  the  ocular  muscles 
are  continuous  with  the  scleral  fibers  in  such  a  manner  that  those 
of  the  straight  muscles  fuse  with  the  meridional  fibers,  while  those 
of  the  oblique  muscles  are  continuous  with  the  equatorial  fibers. 
In  the  sclera  are  many  lymph-channels  communicating  with  those 
of  the  cornea.  They  are  much  coarser  and  more  irregularly  arranged 
than  those  of  the  cornea,  and  in  this  respect  simulate  the  lymph- 
channels  found  in  aponeuroses.  Pigmentation  is  constantly  present 
at  the  corneal  margin,  in  the  vicinity  of  the  optic  nerve  entrance, 
and  also  on  the  surface  next  the  choroid.  The  innermost  pigment 
layer  of  the  sclera  is  lined  by  a  layer  of  flattened  endothelial  cells, 
and  is  regarded  by  some  as  a  separate  membrane,  known  as  the 
lamina  fusca  ;  generally,  however,  it  is  regarded  as  forming  a  part 
of  the  outermost  layer  of  the  choroid  (lamina  suprachoroidea).  The 
external  surface  of  the  sclera  also  presents  a  layer  of  flattened  endo- 
thelial cells,  belonging  to  the  capsule  of  Tenon.  Anteriorly,  the 
mobile  scleral  conjunctiva  is  attached  to  the  sclera  by  a  loose  con- 
nective tissue  containing  elastic  fibers. 

The  cornea  is  inserted  into  the  sclera  very  much  as  a  watch- 
crystal  is  fitted  into  its  frame.  At  the  sclerocorneal  junction  is 
found  an  annular  venous  sinus,  the  canal  of  Schlemm,  which  may 
appear  as  a  single  canal  or  as  several  canals  separated  by  incom- 
plete fibrous  septa.  Anteriorly  and  externally  this  canal  is  bounded 
by  the  cornea  and  sclera ;  internally,  it  is  partly  bounded  by  the 
origin  of  the  ciliary  muscle.      The  sclera  comprises,  therefore,  one- 


TUNICA    FIBROSA    OCULI. 


449 


half  of  the  canal-wall,  and  presents  a  corresponding  circular  sulcus, 
the  so-called  inner  scleral  sulcus. 

The  blood-vessels  of  the  sclera  are  derived  from  the  anterior  and 
posterior  ciliary  vessels.  The  capillaries  enter  either  into  the  ciliary 
veins  or  into  the  venae  vorticosai.  The  numerous  remaining  vessels 
traverse  the  sclera,  extending  to  the  choroid,  iris,  or  scleral  margin. 
At  the  corneal  margin  the  capillaries  form  loops. 


Corneal 
epithelium. 


""   Basal  cells. 


Anterior 
elastic 
membrane. 


Substantia 
propria. 


2.  THE  CORNEA. 

The  cornea  is  made  up  of  the  following  layers  :   (i)  the  ante- 
rior or  corneal  epithelium  ;   (2)  the   anterior  elastic  membrane,   or 
Bowman's  membrane  ;  (3)  the  ground-substance  of  the   cornea,  or 
substantia  propria  ;  (4)  Des- 
cemet's   membrane  ;   (5)  the 
endothelium   of    Descemet's 
membrane. 

At  the  center  of  the 
human  cornea  the  epithe- 
lium consists  of  from  six  to 
eight  layers  of  cells,  being 
somewhat  thicker  near  the 
corneal  margin.  Its  basilar 
surface  is  smooth  and  there 
are  no  connective-tissue  pa- 
pillae. The  basal  epithelial 
layer  is  composed  of  cylin- 
dric  cells  of  irregular  height ; 
the  following  layers  contain 
irregular  polygonal  cells, 
while  the  two  or  three  most 
superficial  layers   consist  of 

tiattened  cells.  The  cells  of  the  corneal  epithelium  are  all  provided 
with  short  prickles,  which  are,  however,  very  difficult  to  demon- 
strate, and  between  are  found  lymph-canaliculi.  The  lower  surfaces 
of  the  basal  cells  also  possess  short  processes  which  penetrate  into 
the  anterior  basement  membrane. 

In  man  the  anterior  elastic  or  Bowman's  membrane  is  quite 
thick,  measuring  from  6  to  8 //  in  thickness  and  is  apparently  homo- 
geneous, but  may  be  separated  into  fibrils  by  means  of  certain 
reagents.  In  structure  it  belongs  neither  to  the  elastic  nor  to  the 
white  fibrous  type  of  connective  tissue,  and  may  be  regarded  as  a 
basement  membrane.  Numerous  nerve-fibers  penetrate  its  pores  to 
enter  the  epithelium.  The  thickness  of  this  membrane  decreases 
toward  the  sclera,  and  it  finally  disappears  about  i  mm.  from  the 
latter. 

The    substantia   propria     consists  of    connective -tissue    fibrils 
grouped  into  bundles  and  lamellae.      Chemically  they  do   not  differ 
29 


Fig.  353. — Section  through  the  anterior  portion 
of  human  cornea  ;   X  S^O- 


450 


THE    EYE. 


from  true  connective-tissue  fibers  (Morochowetz),  but  are  doubly 
refi^acting,  although  the  cornea  as  a  whole  yields  chondrin  and  not 
glutin  on  boiling.  There  are  about  sixty  lamellae  in  the  human 
cornea.  The  fibrils  composing  each  lamella  are  cemented  together 
and  run  parallel  to  one  another  as  well  as  to  the  surface  of  the 
cornea,  but  they  are  so  arranged  that  the  fibrils  of  each  lamella 
cross  those  of  the  immediately  preceding  one  at  an  angle  of  about 
twelve  degrees.  The  lamellae  themselves  are  likewise  closely 
cemented  to  one  another.  The  most  superficial  lamella,  lying  im- 
mediately beneath  the  anterior  elastic  membrane,  is  composed  of 
finer  fibers,  the  course  of  which  is  obHque  to  the  surface  of  the 
cornea.  Between  the  anterior  and  posterior  elastic  membranes  are 
bundles  of  fibers,  which  perforate  the  various  lamellae  of  the  cornea 
and  are  consequently  known  as  the  perforating  or  arcuate  fibers. 
Between   the    lamellae  are    peculiar,  flattened   cells,  possessing 


Lymph-canaliculi. 


Corneal  space. 


Fig.  354. — Corneal  spaces  of  a  dog  ;  X  ^4°- 


irregular  or  lamella-like  processes,  the  fixed  corneal  corpuscles; 

these  lie  in  special  cavities  in  the  ground  substance  of  the  substantia 
propria,  which  are  known  as  corneal  spaces.  In  these  spaces  there 
are  also  found  a  varying  number  of  leucocytes.  By  means  of  vari- 
ous methods  (silver  nitrate  and  gold  chlorid  treatment),  these  corneal 
spaces  may  be  shown  to  be  part  of  a  complicated  lymphatic  system, 
comparable  to  the  lymph-canalicular  system  of  fibrous  connective 
tissue.  This  system  of  canals  is  also  in  communication  with  the 
lymph-channels  at  the  corneal  margin. 

The  posterior  elastic  or  Descemet's  membrane  is  not  so  inti- 
mately connected  with  the  substantia  propria  as  Bowman's  mem- 
brane. It  is  thinnest  at  the  center  of  the  cornea,  and  becomes 
thicker  toward  the  margin.  It  may  be  separated  into  finer  lamellae, 
is  very  elastic,  resists  acids  and  alkalies,  but  is   digested  by  trypsin. 


TUNICA    FIBROSA    OCULI.  45 1 

At  the  periphery — that  is,  at  the  edge  of  the  cornea — Descemet's 
membrane  goes  over  into  the  fibers  of  the  hgamentum  pectinatum. 

The  endothehum  of  Descemet's  membrane  consists  of  low,  quite 
regular  hexagonal  cells,  which  in  certain  vertebrates  (dove,  duck, 
rabbit)  are  peculiar  in  that  a  fibrillar  structure  may  be  seen  in  that 
portion  of  each  cell  nearest  the  posterior  elastic  membrane.  By 
means  of  these  fibers,  not  only  adjacent  cells,  but  also  those  further 
apart,  are  joined  together.  Thus  we  have  here  to  a  marked  degree 
the  formation  of  fibers  which  penetrate  the  cells  and  connect  them 
with  one  another,  conditions  already  met  with  in  the  prickle-cells 
of  the  epidermis. 

The  cornea  is  nonvascular.  In  fetal  life,  however,  the  capil- 
laries from  the  anterior  ciliary  arteries  form  a  precorneal  vascular 
network  immediately  beneath  the  epithelium,  a  structure  which  is 
obliterated  shortly  before  birth  and  only  rarely  seen  in  the  new- 
born. Its  remains  are  found  at  the  corneal  limbus  either  as  an 
episcleral  or  conjunctival  network  of  marginal  capillary  loops.  Fine 
branches  of  the  anterior  ciliary  arteries  extend  superficially  along 
the  sclera  to  the  corneal  margin,  and  form  here  a  network  of  capil- 
laries also  ending  in  loops,  from  which  numerous  veins  arise,  con- 
stituting a  corresponding  network  emptying  into  the  anterior  ciliary 
veins.  The  conjunctival  vessels  likewise  form  a  network  of  mar- 
ginal loops  at  the  corneal  limbus,  and  are  connected  with  the  epi- 
scleral vessels  (Leber).  Under  pathologic  conditions  the  cornea 
may  become  vascularized  from  the  marginal  episcleral  network. 

The  nerves  of  the  cornea  are  derived  from  the  sensory  fibers  of 
the  ciliary  nerves,  which  form  a  plexus  at  the  corneal  margin  ;  from 
this,  nonmedullated  fibers  penetrate  the  cornea  itself  and  form  two 
plexuses,  a  superficial  and  a  gro7md  plexus ;  the  latter  is  distributed 
throughout  the  whole  substantia  propria  with  the  exception  of  its 
inner  third  (Ranvier,  8i).  The  two  plexuses  are  connected  by 
numerous  anastomoses.  At  one  time  it  was  supposed  that  direct 
communication  existed  between  the  corneal  corpuscles  and  the  nerve- 
fibers  of  both  plexuses.  This  view,  however,  contradicts  the  gen- 
erally accepted  neurone  theory. 

Nerve-fibers  from  the  superficial  plexus  pass  through  the  ante- 
rior elastic  membrane  and  form  a  plexus  over  the  posterior  surface 
of  the  epithelium,  known  as  the  subepithelial  plexus.  From  the  lat- 
ter nerve-fibers  extend  between  the  epithelial  cells,  terminating  in 
telodendria  with  long  slender  nerve-fibrils,  which  end  in  small 
nodules.  Many  of  the  fibrils  reach  almost  to  the  surface  of  the 
epithelium  (Rollet,  71;   Ranvier,  81 ;   Dogiel,  90). 

Smirnow  (1900)  has  described  a  rich  nerve-supply  for  the  sclera, 
consisting  of  both  medullated  sensory  fibers  and  nonmedullated 
sympathetic  fibers,  derived  mainly  from  the  ciliary  nerves.  The 
sympathetic  fibers  supply  the  blood-vessels ;  the  sensory  fibers  ter- 
minate in  free  endings  between  the  connective-tissue  lamellae. 


452 


THE    EYE. 


D.  THE  VASCULAR  TUNIC  OF  THE  EYE. 

THE  CHOROID,  THE  CILIARY  BODY,  AND  THE  IRIS. 

From  without  inward  the  following  layers  may  be  differentiated 
in  the  choroid  :  (i)  the  lamina  suprachoroidea  ;  (2)  the  la7ni?ia  vas- 
culosa  Halleri ;  (3)  the  lamina  choj'iocapillaris  ;  and  (4)  the  glassy 
layer,  or  vitreous  membrane. 

The  lamina  suprachoroidea  consists  of  a  number  of  loosely 
arranged,  branching  and  anastomosing  bundles  and  lamellae  of 
fibrous  tissue,  joined  directly  to  the  sclera.  These  bundles  and 
lamellae  consist  of  white  fibrous  connective  tissue  containing  numer- 
ous elastic  fibers,  among  which  a  few  connective-tissue  cells  are  dis- 
tributed. Pigment  cells  are  also  present  in  varying  numbers.  The 
bundles  and  lamellae  are  covered  by  endothelial  cells,  and  the  spaces 
and  clefts  between  them,  and  between  the  lamina  suprachoroidea 
and  the  lamina  fusca,  constitute  a  system  of  lymph-channels — the 
perichoroidal  lymph-spaces. 


Sclera. 


Lamina    supra- 
choroidea. 


Lamina    vaseu- 
losa  Halleri. 


Lamina  chorio- 
capillaris. 
Glassy  layer. 


Fig-  355- — Section  through  the  human  choroid  ;   X  '^2P' 

The  lamina  vasculosa  of  the  choroid  is  also  composed  of  simi- 
lar lamellae,  which,  however,  are  more  closely  arranged.  The  blood- 
vessels constitute  the  principal  portion  of  this  layer,  the  vessels 
being  of  considerable  caliber,  not  capillaries.  They  are  so  distrib- 
uted that  the  larger  vessels,  the  veins,  occupy  the  outer  layer  of 
the  lamina  vasculosa.  The  venous  vessels  converge  toward  four 
points  of  the  eyeball,  forming  at  the  center  of  each  quadrant  one 
of  the  four  vence  vorticoscs.  The  arteries,  on  the  other  hand,  describe 
a  more  meridional  course. 


THE    VASCULAR    TUNIC    OF    THE    EYE.  453 

In  the  inner  portion  of  this  layer  is  found  a  narrow  zone, — in 
the  human  eye  only  about  lO /i  in  thickness, — consisting  largely 
of  elastic  fibers  and  free  from  pigment  cells,  known  as  the  boundary 
zone.  This  zone  is  somewhat  thicker  in  many  mammals,  and  in 
some  of  these  presents  a  characteristic  structure.  In  the  eyes  of 
ruminants  and  horses  this  zone  consists  of  several  layers  of  con- 
nective-tissue bundles,  and  is  known  as  the  tapeUan  fibrosiim.  It 
gives  the  peculiar  luster  often  seen  in  the  eyes  of  these  animals.  In 
the  eyes  of  Carnivora  this  zone  consists  of  several  layers  of  endothe- 
lioid  cells,  containing  in  their  protoplasm  numerous  small  crystals 
and  forming  the  iridescent  layer  known  as  the  tapettun  celluloswii. 

The  lamina  choriocapillaris  contains  no  pigment  and  consists 
principally  of  capillary  vessels,  which  form  an  especially  dense  net- 
work in  the  neighborhood  of  the  macula  lutea.  As  the  venous  cap- 
illaries become  confluent  and  form  smaller  veins,  the  latter  arrange 
themselves  in  long,  radially  directed  networks,  and  form  in  this  way 
the  more  or  less  pronounced  stellidcE  vascidoscE  (Winslowii). 

The  vitreous  or  glassy  membrane  is  a  very  thin  (2  //)  homo- 
geneous membrane  which  shows  on  its  outer  surface  the  impressions 
of  the  vessels  composing  the  lamina  choriocapillaris,  and  on  its 
inner  surface  those  of  the  pigment  epithelium  of  the  retina. 

At  the  ora  serrata  the  choroid  changes  in  character ;  from  this 
region  forward,  the  choroidal  tissue  assumes  more  the  appearance  of 
ordinary  connective  tissue,  and  the  choriocapillary  layer  is  wanting. 

The  region  of  the  vascular  coat  extending  from  the  ora  serrata 
to  the  base  of  the  iris  is  known  as  the  ciliary  body.  Its  posterior 
portion,  about  4  mm.  broad,  the  orbiadus  cdiaris,  is  slightly  thicker 
than  the  choroid,  and  presents  on  its  inner  surface  numerous  small 
folds,  meridionally  placed,  consisting  of  connective  tissue  and  blood- 
vessels. Anterior  to  the  orbiculus  ciliaris  the  ciliary  body  is  thick- 
ened by  a  development  of  nonstriated  muscle — the  ciliary  muscle 
(see  below)  ;  and  on  the  inneir  surface  of  this  annular  thickening  are 
placed  about  seventy  triangular  folds,  meridionally  arranged — the 
ciliary  processes.  The  attached  border  of  these  processes  measures 
from  2  to  3  mm.  The  anterior  border  attains  a  height  of  about 
I  mm.  On  and  between  these  folds  are  found  numerous  small 
secondary  folds  or  processes  of  irregular  shape.  The  ciliary  pro- 
cesses consist  of  fibrous  connective  tissue  and  numerous  smaller 
and  larger  vessels,  which  have  in  the  main  a  meridional  arrange- 
ment. The  vitreous  membrane  extends  over  the  ciliary  body,  attain- 
ing in  the  region  of  the  ciliary  processes  a  thickness  of  3  //  or  4  //. 
Internal  to  the  vitreous  membrane,  the  ciliary  body  is  covered  by 
a  double  layer  of  epithelial  cells,  the  continuation  forward  of  the 
retina  (^pars  ciliaris  rctincE).  Of  these,  the  outer  layer  is  composed 
of  cells,  which  are  deeply  pigmented,  and  are  of  cubic  or  short 
columnar  shape,  and  derived  from  the  outer  layer  of  the  secondary 
optic  vesicle,  while  the  cells  of  the  inner  layer  are  nonpigmented 
and  of  columnar  shape,  and  are  developed  from  the  inner  layer  of 
the  secondary  optic  vesicle.      In  the  region  of  the  ciliary  processes 


454 


THE    EYE. 


their  epithelial  hning  presents  here  and  there  evaginations  of  glan- 
dular appearance,  lined  by  the  unpigmented  cells.  These  evagina- 
tions are  known  as  ciliary  glands,  and  to  them  is  attributed — in 
part,  at  least — the  secretion  of  the  fluid  found  in  the  anterior  cham- 
ber of  the  eye  ;  it  is,  however,  still  a  question  as  to  whether  these 
structures  are  to  be  regarded  as  true  glands  or  simply  as  depressions 
or  crypts  in  the  epithelium. 

The  ciliary  muscle  is  bounded  anteriorly  (toward  the  anterior 
chamber)  by  the  ligamentum  pectinatum  iridis,  externally  by  the 
cornea  and  sclera,  posteriorly  by  the  orbiculus  ciliaris,  and  inter- 
nally by  the  ciliary  processes.  It  consists  of  nonstriated  muscle- 
fibers  in  the  majority  of  vertebrates.  This  muscle  is  divided  into 
three  portions.  The  outer  or  meridional  division  extends  from  the 
posterior  elastic  lamina  of  the  cornea  and  its  continuation,  forming 
the  inner  wall  of  the  sinus  venosus  sclerae,  to  the  posterior  portion 
of  the  ciliary  ring.   The  origin  of  the  middle  division  is  identical  with 


Loose  connec- 
tive tissue  of 
the  conjunc- 
tiva. 


Conjunctiva. 


Corneal  epithe- 
lium. 

Substantia  pro- 
pria. 


Descemet's 
membrane. 
^  Canal  of 

Schlemm. 

Iris. 
-i.  Pigment  layer. 

Meridional  fibers. 
Radial  fibers. 
Müller's  fibers. 


Sclera.  Processus  ciliares. 

Fig.  356. — Meridional  section  of  the  human  ciliary  body  ;  X  20. 

that  of  the  outer,  but  its  fibers  (assuming  that  we  have  before  us  a 
meridional  section)  spread  out  like  a  fan,  and  occupy  a  large  area 
at  their  insertion  into  the  ciliary  ring  and  ciliary  processes.  The 
radial  course  of  these  fibers  is  interrupted  by  circular  bundles.  The 
third  or  inner  division  i^fibrcE  circulares,  fibers  of  Müller)  is  situated 
between  the  ligamentum  pectinatum,  the  ciliary  processes,  and  the 
middle  portion  of  the  muscle  just  mentioned,  and  is  thus  near  the 
base  of  the  iris. 

Between  the  ciliary  muscle  and  the  posterior  elastic  membrane 
of  the  cornea  is  an  intermediate,  richly  cellular  tissue,  which  maybe 
regarded  as  a  continuation  of  this  elastic  membrane,  and  which 
forms  a  part  of  the  wall  of  the  sinus  venosus.  Another  structure 
internal  to  the  foregoing  and  directed  posteriorly  is  the  ligamentum 
pectinatum  iridis,  which  encircles  the  anterior  chamber  and  is  a  con- 
tinuation of  Descemet's  membrane  to  the  base  of  the  iris.      It  con- 


THE    VASCULAR    TUNIC    OF    THE    EYE.  455 

sists  of  fibers  and  lamellae  lined  by  endothelial  cells,  and  bounds 
certain  intercommunicating  spaces  lying  in  the  ligament,  known  as 
the  spaces  of  Fontana.  The  latter  communicate  on  the  one  side 
with  the  perivascular  spaces  of  the  sinus  venosus  sclerae  (canal  of 
Schlemm),  and  on  the  other  with  the  anterior  chamber. 

The  iris  must  be  looked  upon  as  a  continuation  of  the  choroid, 
and  is  connected  at  its  anterior  peripheral  portion  with  the  ligamen- 
tum  pectinatum.  The  iris  possesses  the  following  layers,  beginning 
anteriorly  :  (i)  the  anterior  endothelium;  (2)  the  ground  layer,  or 
stroma  of  iris,  together  with  the  sphincter  muscle  of  the  pupil;  and 
(3)  the  two-layered,  pigmented  epithelium — the  pars  iridica  retinae, 
of  which  the  anterior  is  in  part  replaced  by  a  peculiar  muscle  tissue, 
developed  from  the  ectoderm  and  forming  the  dilator  of  the  pupil. 

The  anterior  endothelium  is  a  single  layer  of  irregularly  polyg- 
onal, nonpigmented  cells,  and  is  directly  continuous  with  the 
endothelium  of  the  pectinate  ligament. 

The  ground-layer  or  stroma  of  iris  consists  anteriorly  of  a  fine 
reticulate  tissue  rich  in  cellular  elements  (reticulate  layer).  The 
remaining  strata  which  form  the  bulk  of  the  ground-layer  consti- 
tute its  vascular  layer.  The  vessels  are  here  peculiar  in  that  they 
are  covered  by  coarse,  circular,  connective -tissue  fibers  forming  vas- 
cular sheaths.  There  is  also  an  entire  absence  of  muscular  tissue 
in  the  vessel  walls.  The  nerves,  too,  are  enveloped  by  a  dense  con- 
nective tissue.  In  all  eyes  (except  the  albinotic)  pigment  is  found 
in  the  connective  tissue. 

On  the  posterior  inner  surface  of  the  ground-layer  is  a  band  of 
smooth  muscle-fibers  encircling  the  pupil — the  sphincter  imisde  of 
the  pupil.  Posterior  to  this  and  in  intimate  relation  with  the  layer 
of  pigmented  epithelium  covering  the  posterior  surface  of  the  iris  is  a 
layer  of  spindle-shaped  cells  having  a  radial  arrangement  and  contain- 
ing pigment.  Closer  microscopic  inspection  reveals  the  fact  that  in  all 
probability  these  elements  represent  muscular  tissue.  Here,  there- 
fore, we  have  to  deal  with  a  dilator  muscle  of  the  pupil.  There  has 
been  much  discussion  as  to  the  existence  and  structure  of  this  muscle. 
Recent  investigations  (Szili)  indicate  that  it  is  developed  from  the  outer 
layer  of  the  secondary  optic  vesicle. 

The  posterior  epithelium  is  the  direct  continuation  of  the  two 
epithelial  layers  of  the  ciliary  body,  and  represents  the  anterior  por- 
tion of  the  secondary  optic  vesicle,  the  two  layers  being  continuous 
at  the  margin  of  the  pupil.  In  the  iris  both  layers  of  cells,  so  far  as 
they  exist,  are  pigmented. 

The  arteries  of  the  choroid  are  derived  from  the  short  posterior 
ciliary,  the  long  ciliary,  and  the  anterior  ciliary  arteries.  The  short 
posterior  ciliary  arteries  penetrate  the  sclera  in  the  vicinity  of  the  optic 
nerve,  where  they  anastomose  with  branches  from  the  retinal  vessels, 
and  spread  through  the  choroid,  where  they  form  the  choriocapillary 
layer.  The  long  posterior  ciliary  arteries  (a  mesial  and  a  lateral) 
penetrate  the  sclera  and  course  forward  between  choroid  and  sclera  to 
the  ciliary  body,  forming  there  the  cir cuius  arteriosus  iridis  major;  they 


456 


THE    EYE. 


also  supply  the  ciliary  muscle,  the  ciliary  processes,  and  the  iris,  and 
anastomose  in  the  ciliary  ring  with  the  branches  of  the  short  pos- 
terior and  anterior  ciliary  arteries.  The  latter  lie  beside  and  partly 
within  the  straight  ocular  muscles,  penetrating  the  latter  at  the  an- 
terior margin  of  the  sclera  ;  they  give  off  branches  to  the  circulus 
arteriosus  iridis  major  and  to  the  ciliary  muscles,  anastomosing  at 
the  same  time  with  the  posterior  ciliary  arteries.  (Compare  Figs. 
352  and  357.)  Within  the  iris  the  blood-vessels  generally  take 
a  radial  direction,  but  also  anastomose  with  one  another,  forming 
capillaries,  and  subsequently  the  circulus  arteriosus  iridis  minor  at 
the  inner  pupillary  margin.  From  the  region  supplied  by  the 
posterior  ciliary  arteries  most  of  the  blood  is  carried  toward  the 
vorticose  veins.  The  anterior  ciliary  veins  convey  the  blood  com- 
ing from  the  arteries  of  the  same  name.  Into  these  veins  is  also 
poured  the  blood  from  the  veins  lying  in  the  canal  of  Schlemm, 
the  canal  itself  being  in  reality  an  open  venous  sinus.  Besides  this, 
these  veins  convey  also  venous  blood  from  the  conjunctiva  (Leber). 
The  nonstriated  muscle  of  the  ciliary  body  and  iris  receives  its 
innervation  through  sympathetic  nerve-fibers,  neuraxes  of  sympa- 
thetic neurones,  the  cell-bodies  of  which  are  situated  either  in  the 
ciliary  ganglia  or  in  the  superior  cervical  ganglia.  The  neuraxes 
of  the  sympathetic  cells  forming  the  ciliary  ganglia  form  the  short 

ciliary  nerves,  which  pierce 
the  sclera  in  the  neighbor- 
hood of  the  optic  nerve  and 
pass  forward,  to  terminate  in 
the  muscle  of  the  ciliary  body 
and  the  sphincter  muscle  of 
the  pupil.  Stimulation  of 
these  nerves  causes  a  con- 
traction of  the  ciliary  muscle 
and  a  closure  of  the  pupil. 
The  cell-bodies  of  the  sympa- 
thetic neurones  forming  the 
ciliary  ganglia  are  surrounded 
by  pericellular  plexuses,  the 
terminations  of  small  medul- 
lated  nerve -fibers  (white  rami 
fibers)  which  reach  the  ciliary 
ganglia  through  the  oculo- 
motor nerves.  Neuraxes  of 
sympathetic  neurones,  the 
cell-bodies  of  which  are  sit- 
uated in  the  superior  cervical 
ganglia,  reach  the  eye  through 
the  cavernous  plexuses,  to  ter- 
minate, it  is  thought, — in  part, 
at  least, — in  the  dilator  of  the 
iris,   since  stimulation   of  these   nerves   causes   a   dilatation   of  the 


Margin  of 
pupil. 


»Choroid. 


Fig.  357.^ — Injected  blood-vessels  of  thehuman 
choroid  and  iris ;  X  7- 


THE  INTERNAL  OR  NERVOUS  TUNIC  OF  THE  EYE.      457 

pupils.  The  cell-bodies  of  these  sympathetic  neurones  are  sur- 
rounded by  pericellular  plexuses,  the  terminations  of  white  rami 
fibers  which  leave  the  spinal  cord  through  the  first,  second,  and 
third  thoracic  nerves  (Langley),  and  which  reach  the  superior  cer- 
vical ganglia  through  the  cervical  sympathetic. 

Melkirch  and  Agababow  have  shown  that  numerous  sensory 
nerves  terminate  in  free  sensory  endings  in  the  connective  tissue 
of  the  ciliary  body  and  iris.  The  sensory  nerve-supply  of  the  iris 
is  especially  rich. 


E.  THE  INTERNAL  OR  NERVOUS  TUNIC  OF 
THE  EYE, 

This  tunic  is  composed  of  two  layers  :  the  outer,  or  stratum  pig- 
mettti  ;  and  the  inner,  or  retina. 

J.  THE  PIGMENT  LAYER. 

The  pigment  layer  develops,  as  we  have  seen,  from  the  outer 
layer  of  the  secondary  optic  vesicle.  It  consists  of  regular  hexa- 
gonal cells,  12  //  to  18  /i  in  length  and  9  /i  in  breadth,  which  con- 
tain black  pigment  in  the  form  of  granules.  The  inner  surfaces 
of  these  cells  possess  long,  thread-like  and  fringe-like  processes, 
between  which  project  the  external  segments  of  the  rods  and  cones 
of  the  retina,  yet  to  be  described.  The  nuclei  of  the  pigment  cells 
lie  in  the  outer  ends  of  the  cells,  the  so-called  basal  plates,  and  are 
not  pigmented.  The  distribution  of  the  pigment  varies  according  to 
the  illumination  of  the  retina.  If  the  latter  be  darkened,  the  pig- 
ment collects  at  the  outer  portion  of  each  cell ;  if  illuminated,  the 
pigment  is  evenly  distributed  throughout  the  whole  cell.  The  pig- 
ment granules  are  therefore  mobile  (Kühne,  79). 

2.  THE  RETINA. 

The  retina  has  not  the  same  structure  throughout.  In  certain 
areas  peculiarities  are  noticeable  which  must  be  described  in  detail  ; 
such  areas  are  :  (i)  the  macula  lutea  ;  (2)  the  region  of  the  papilla 
(papilla  nei-vi  optici)  ;  (3)  the  ora  serrata ;  (4)  the  pars  ciliaris 
retinae  ;  and  (5)  the  pars  iridica  retinae. 

We  shall  begin  with  the  consideration  of  that  portion  of  the 
retina  lying  between  the  ora  serrata  and  the  optic  papilla  (exclusive 
of  the  macula  lutea). 

From  without  inward,  we  differentiate:  (i)  the  layer  of  vis- 
ual cells,  including  the  outer  nuclear  layer ;  (2)  the  outer  molecu- 
lar (plexiform)  layer;  (3)  the  inner  nuclear  or  granular  layer;  (4) 
the  inner  molecular  (plexiform)  layer  ;  (5)  the  ganglion-cell  layer  ; 
(6)  the  nerve-fiber  layer.      Besides  these,  we  must  also  consider  the 


458 


THE    EYE. 


supporting  tissue  of  the  retina  and  Miiller's  fibers,  together  with  the 
internal  and  external  limiting  membranes. 

The  visual  cells  are  either  rod-visual  cells  or  cone-visual  cells. 
The  rod=visual  cells  consist  of  a  rod  and  a  rod-fiber  with  its 
nucleus.  The  rod  (40  //to  50  /i  in  length)  consists  of  two  seg- 
ments, an  outer  and  an  inner,  the  former  of  which  is  doubly  refrac- 
tive and  may  be  separated  into  numerous  transverse  discs  by  the 
action  of  certain  reagents.  The  inner  is  less  transparent  than  the 
outer  segment,  and  its  inner  end  shows  a  fine  superficial  longitu- 
dinal striation  due  to  impressions  from  the  fiber-baskets  formed  by 
Miiller's  fibers.      In  the  lower  classes  of  vertebrates  a  rod-ellipsoid 


Layer  of  nerve- 
fibers. 


Ganglion-cell  layer.    ---T/ 


Inner  molecular 
layer. 


Inner  nuclear  layer. 

Outer  molecular 
layer. 


Outer  nuclear 
layer. 

Ext.  limiting  mem- 
brane. 
Inner  segment  of 

rod. 
Inner  segment  of  — 
cone. 

Outer  segment  of 

cone. 
Outer  segment  of 

rod. 


Fig.  358. — Section  of  the  human  retina  ;  X  7°0' 


(a  fibrillar  structure)  may  easily  be  demonstrated  in  the  outer  region 
of  each  inner  portion  ;  in  many  mammalia  and  in  man  the  demon- 
stration of  this  is  more  difficult.  This  structure  is  a  planoconvex, 
longitudinally  striated  body,  the  plane  surface  of  which  is  coincident 
with  the  external  surface  of  the  inner  segment,  its  inner  convex  sur- 
face lying  at  the  junction  of  the  outer  and  middle  thirds  of  the  inner 
segment.  The  rod-fibers  extend  as  far  as  the  outer  molecular  layer 
of  the  retina,  where  they  end  in  small  spheric  swellings.  The  nuclei 
of  the  rod-visual  cells  are  found  at  varying  points  within  the  rod- 
fibers,  but  rarely  close  to  the  inner  segment.  When  treated  with 
certain  fixing  agents  and  stains,  the  rod-nuclei  of  certain  animals  (cat 
and  rabbit)  are  seen  to  show  several  zones,  which  stain  alternately 


THE    INTERNAL    OR    NERVOUS    TUNIC    OF    THE    EYE.  459 

light  and  dark  (striation  of  the  rod-nuclei).      This  striation  is  not  gen 
e?ally  observed  in  the  rod-nuclei  of  the  human  retina. 

The  cone=visual  cells  consist,  similarly  to  the  rod-visual  cells, 
of  a  cone  and  a  cone-fiber  with  its  nucleus.  The  cone  (15  [x  to 
25  /i  in  length)  is,  as  a  whole,  shorter  than  the  rod,  and  its  inner 
segment  is  considerably  broader  than  that  of  the  rod.  The  cone 
eUipsoid  comprises  the  outer  two -thirds  of  the  inner  segment,  and 
the  outer  segment  has  a  more  conical  shape.  The  cone-fiber  like- 
wise extends  as  far  as  the  outer  molecular  layer,  where  it  ends  in 
a  branched  basal  plate.  Its  somewhat  larger  nucleus  is  always 
found  in  the  vicinity  of  the  inner  segment  of  the  cone.  The 
inner  surfaces  of  the  inner  segments,  not  only  of  the  cone-cells,  but 
also  of  the  rod-visual  cells,  lie  in  one  plane,  corresponding  to  the 
external  limiting  membrane,  a  structure  composed  of  the  sustenta- 
cular  fibers  of  Müller.  The  rod-fibers  and  cone-fibers,  with  the 
nuclei  of  the  rod-  and  cone-visual  cells,  lie  between  the  external 
limiting  membrane  and  the  outer  molecular  layer.  It  will  be 
observed,  therefore,  that  the  visual  cells  include  the  layer  of  rods 
and  cones  and  the  outer  nuclear  layer. 

The  outer  molecular  layer  consists  :  (i)  of  the  ramifications  of 
Müller' s  fibers  ;  (2)  of  the  knob  and  tuft-Hke  endings  of  the  visual 
cells  ;  and  (3)  of  the  dendritic  processes  of  the  bipolar  cells  of 
the  inner  nuclear  layer.  These  structures  will  be  considered  more 
in  detail  in  discussing  the  relations  of  the  elements  comprising  the 
retina. 

The  inner  nuclear  layer  contains:  (i)  the  nucleated  stratum 
of  Müller's  sustentacular  fibers  ;  (2)  g;anglion  cells  situated  in^  the 
outer  region  of  the  layer  and  extending  in  a  horizontal  direction  ; 
(3)  bipolar  ganglion  cells  with  oval  nuclei,  densely  placed  at  various 
depths  of  the  layer  and  vertical  to  it ;  (4)  amacrine  cells  (neurones, 
apparently  without  neuraxes)  lying  close  to  the  inner  margin  of 
the  layer  and  forming  with  their  larger  nuclei  a  nearly  continuous 
layer  of  so-called  spongioblasts.  The  numerous  processes  of  these 
spongioblasts  lie  in  the  inner  molecular  layer,  the  composition  of 
which  will  be  further  discussed  later. 

The  ganglion-cell  layer  of  the  optic  nerve  consists,  aside  from 
centrifugal  neuraxes  and  the  fibers  of  Müller,  which  are  here 
present,  of  multipolar  ganglion  cells,  the  dendrites  of  w^hich  extend 
outward  and  the  neuraxes  of  which  are  directed  toward  the  optic 
nerve-fiber  layer.  These  cells  vary  in  size,  and  their  nuclei  are 
typical,  being  relatively  large,  deficient  in  chromatin,  and  always 
provided  with  large,  distinct  nucleoli.  In  man  the  optic  nerve- 
fibers  of  the  retina  are  nonmedullated. 

All  these  structures  are  typical  of  that  portion  of  the  retina 
lying  behind  the  ora  serrata.  The  retina  in  the  vicinity  of  the  optic 
papilla  and  macula  lutea  must  be  taken  up  separately. 


460 


THE    EYE. 


3.  REGION  OF  THE  OPTIC  PAPILLA. 

The  optic  papilla  is  the  point  of  entrance  of  the  optic  nerve 
into  the  retina.  At  the  center  of  the  papilla,  in  the  region  where 
the  nerve-fibers  spread  out  radially  in  order  to  supply  the  various 
areas  of  the  retina,  is  a  small,  funnel-shaped  depression,  the  physi- 
ologic excavation.  The  fibers  of  the  optic  nerve  lose  their  medullary 
sheaths  during  their  passage  through  the  sclera  and  choroid,  and  then 
continue  to  the  inner  surface  of  the  retina,  over  which  they  spread  in 
a  layer  which  gradually  becomes  thinner  toward  the  ora  serrata.  On 
account  of  the   deflection  of  the  nerve-fibers,  and   because,  during 


Physiologic  excaTation. 


Layer  of  nerve-fibers..., ! 
Inner  molecular  layer.. _  j 
Inuer  nuclear  layer.  .J^^-.y 

Outer  molecular  layer -^^^ 

Outer  nuclear  layer -y-'' 

Rods  and  coues.-' 
Pigment  layer.  .- 
Sclcra.•■ 


Lamina  cribrosa.* 


Fig.  359. — Section  through  point  of  entrance  of  human  optic  nerve  ;    X  40. 

their  passage  through  the  sclera,  they  lose  their  medullary  sheaths 
at  one  and  the  same  point,  the  optic  nerve  becomes  suddenly 
thinner.  The  result  is  a  deeply  indented  circular  depression  in  this 
region.  On  this  depression  border  the  three  ocular  tunics.  At  this 
point  the  retina  is  interrupted,  the  outer  layers  extending  to  the  bot- 
tom of  the  depression,  while  the  inner  cease  at  its  margin.  In  many 
cases  the  outer  layers  of  the  retina  are  separated  from  the  optic  nerve 
by  a  thin  lamina  of  supporting  tissue  (intermediate  tissue). 


4.  REGION  OF  THE  MACULA  LUTEA. 

At  the  center  of  the  macula  lutea  is  a  trough -like  depression, 
the  fovea  centralis,  the  deepest  part  of  which,  the  fundus,  lies  very 
close  to  the  visual  axis.  Here  the  layers  of  the  retina  are  practic- 
ally reduced  to  the  cone-visual  cells.  The  margin  of  this  depression 
is  somewhat  thickened,  owing  to  an  increase  in  the  thickness  of  the 
nerve-fiber  and  ganglion-cell  layers.  Toward  the  fundus  of  the  fovea 
each  of  the  four  inner  retinal  layers  becomes  reduced  in  thickness, 
the  inner  layer  first  and  the  three  others  in  their  order :  the  inner 
molecular  layer,  however,  seems  to  extend  as  far  as  the  fundus.  As 
we  have  seen,  only  the  cone-visual  cells  are  found  in  the  fovea  cen- 
tralis, there  being  an  entire  absence  of  the  rod-visual  cells.  Since 
the  nuclei  of  the  cone-visual  cells  are  in  the  immediate  neighborhood 


THE  INTERNAL  OR  NERVOUS  TUNIC  OF  THE  EYE. 


461 


of  the  cones,  and  since  the  cone-fibers,  in  order  to  reach  the  outer 
molecular  layer,  must  here  describe  a  curve,  there  arises  a  peculiar 
^ayer,  composed  of  obliquely  directed  fibers,  known  as  the  02iter 
fiber-layer  or  Hcnle's  fiber  layer.  In  other  words,  the  fibers  of  this 
region  are  more  distinctly  seen  because  they  are  not  covered  by  the 
rod-nuclei  and  rod-fibers. 


Layer    of 

nerve-fibers  I 
Ganglion-cell 

layer.  | 

Inner  molecu- 
lar layer.  . 

Inner  nuclear  | 
layer. 

Outer   molec-  '^ 

ular  layer.  r 

Outer  fibrous  I 

layer.  1 

Outer  nuclear  L 

layer.  L 


Fovea  centralis. 


,,,.,,., _,,.._,,   ..,:,.,.. ..._,_...^,^_  _  ,,:, .„ ■' -Jii 

Fig.  360. — Section  through  human  macula  lutea  and  lovea  centralis  ;  X  ^S^-  As 
a  result  of  treatment  with  certain  reagents,  the  fovea  centralis  is  deeper  and  the  margin 
more  precipitous  than  during  life. 

The  yellowish  color  of  the  fovea  centralis  is  due  to  pigment  held 
in  solution  within  the  layers  of  the  retina.  The  cone-visual  cells 
themselves  contain  no  pigment. 


5.  ORA  SERRATA,  PARS  CILIARIS  RETINAE,  AND  PARS  IRIDICA 

RETINAE. 

In  the  region  of  the  ora  serrata  the  retina  suddenly  becomes 
thinner.  As  seen  from  the  inner  surface  of  the  retina,  its  decrease 
presents  the  appearance  of  an  irregular  curve  rather  than  of  the 
segment  of  a  sphere.  Shortly  before  the  retina  terminates,  its  layers 
become  markedly  reduced,  certain  ones  disappearing  entirely ;  first 
the  nerve-fiber  layer,  then  the  ganglion-cell  layer  and  cone-  and  rod- 
visual  cells,  their  place  being  taken  by  an  indifferent  epithelium.. 
The  inner  molecular  layer  of  the  retina  gradually  loses  the  pro- 
cesses which  penetrate  inward.  In  the  region  of  the  ora  serrata  the 
sustentacular  fibers  are  markedly  developed.  Relatively  large  hol- 
low spaces  are  often  found  in  the  retina  at  the  ora  serrata ;  they  are 
thought  to  be  due  to  edema. 

The  pars  ciliaris  retinae  consists  essentially  of  two  simple 
layers  of  cells,  of  which  the  external  represents  the  pigment  layer 
and  the  internal  the  inner  epithelium  of  the  secondary  optic  vesicle. 
In  the  pars  iridica  retinae  the  arrangement  is  similar ;  here  both 
layers  are  pigmented. 


4^2  THE    EYE. 

6.  MÜLLER'S  FIBERS  OF  THE  RETINA. 

Genetically,  the  sustentacular  fibers,  or  fibers  of  Müller,  in  the 
retina  are,  like  the  whole  retina,  of  ectodermic  origin,  and  repre- 
sent a  highly  developed  form  of  neurogliar  tissue.  They  penetrate 
the  retina  from  within  and  extend  as  far  as  the  inner  segments  of 
the  rods  and  cones.  Each  fiber  represents  a  long,  greatly  modified 
epithelial  cell,  terminating  in  one  or  more  broad  basal  plates,  which 
come  in  contact  with  those  of  adjacent  fibers,  thus  forming  a  sort 
of  membrane — the  internal  limiting  membrane .  Owing  to  its 
marked  plasticity,  each  fiber  presents  certain  peculiarities  within 
the  various  layers  of  the  retina  through  which  it  penetrates. 
Thus,  within  the  molecular  layers  the  fiber  is  provided  with  trans- 
versely directed  processes  and  platelets.  Within  the  nuclear  layers, 
on  the  other  hand,  are  numerous  lateral  indentations,  which  corre- 
spond to  the  impressions  produced  by  the  cells  of  these  layers.  At 
the  inner  surface  of  the  cones  and  rods  the  fibers  terminate  in  end- 
plates,  which  represent  cuticular  formations,  and,  blending  with  one 
another,  form  a  single  membrane — the  external  limiting  m.embrane. 
This  membrane  is  perforated  by  the  rod-fibers  and  cone-fibers.  The 
end-plates  of  the  fibers  give  off  externally  short,  inflexible  fibrils, 
which  form  the  fiber-baskets  containing  the  basilar  portions  of  the 
inner  segments  of  the  rods  and  cones.  {Vid.  Fig.  361.)  Miiller's 
fibers  do  not  appear  as  fibers  in  chrome-silver  preparations,  but  as 
complicated  cellular  structures,  as  above  depicted.  In  preparations 
of  the  retina,  stained  in  a  differential  neuroglia  stain  (Benda's 
method),  clearly  defined  fibers,  stained  after  the  manner  of  neuroglia 
fibers,  may  be  differentiated.  These  fibers  are  in  contact  with  or 
are  imbedded  in  the  protoplasm  of  the  Miiller's  fibers. 

7.    THE    RELATIONS  OF  THE  ELEMENTS  OF  THE  RETINA  TO 

ONE  ANOTHER. 

We  shall  now  take  up  the  relationships  existing  between  the 
various  elements  of  the  retinal  strata,  giving  the  theories  now 
generally  accepted  and  based  on  observations  made  with  the  Golgi 
and  methylene-blue  methods,  and  more  particularly  on  the  investi- 
gations of  Ramon  y  Cajal  (see  diagram.  Fig.  361)  : 

1 .  The  inner  processes  of  the  rod-visual  cells  end,  as  a  rule,  in 
small  expansions  within  the  outer  inolecular  layer,  in  which  also  the 
processes  of  the  cone-visual  cells  terminate  in  broader  branched 
pedicles.  In  this  layer  also  are  situated  the  terminal  arborizations 
of  the  dendrites  and  neuraxes  of  certain  cells  belonging  to  the  inner 
nuclear  layer. 

2.  The  inner  nuclear  layer  consists,  as  we  have  seen,  {a)  of  bipolar 
cells,  which  constitute  the  principal  portion  of  this  layer,  ib)  of  hori- 
zontally placed  cells  lying  immediately  beneath  the  outer  molecular 
layer,  and  {c)  of  the  layer  of  spongioblasts  situated  at  the  junction 


THE    INTERNAL    OR    NERVOUS    TUNIC    OF    THE    EYE. 


463 


of  the  inner  nuclear  with  the  inner  molecular  layer.  The  bipolar  cells 
comprise  the  following  :  (a)  Bipolar  cells  of  the  rod-visual  cells  the 
dendrites  of  which  intertwine  around  the  basilar  portions  of  the  rod- 
visual  cells,  and  the  neuraxes  of  which  end  in  telodendria  in  the  neigh- 
borhood of  the  cell-bodies  of  the  nerve-cells  of  the  ganglion-cell  layer. 
(/9)  Bipolar  cells  of  the  cone-visual  cells.     The  dendrites  of  these  cells, 


2,? 

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which  also  end  in  the  outer  molecular  layer,  are  there  in  relation  to 
the  basilar  processes  of  the  cone-fibers.  Their  neuraxes  come  in 
contact,  by  means  of  terminal  arborizations,  with  the  dendrites  of  the 
ganglion  cells  of  the  ganglion-cell  layer  at  varying  depths  of  the 
inner  molecular  layer.  (;')  Besides  these,  there  are  also  bipolar 
cells  which,  as  in  the  case  of  o  and  ß,  form  contact  with  the  rod-  and 


464  THE    EYE. 

cone-visual  cells,  but  end  on  the  cell-bodies  of  the  ganglion  cells 
of  the  ganglion-cell  layer.  The  horizontal  cells  send  their  dendrites 
into  the  outer  molecular  layer,  while  their  neuraxes  extend  hori- 
zontally and  give  off  numerous  collaterals  to  the  same  layer,  ending 
there  in  telodendria.  These  cells  are  of  two  varieties:  the  smaller,  in- 
directly connecting  the  cone-visual  cells  with  one  another  by  means 
of  their  dendrites  and  neuraxes  ;  and  the  larger,  more  deeply  situated 
cells,  connecting  in  a  similar  manner  the  basilar  ends  of  the  rod- 
visual  cells.  A  few  cells  of  the  second  variety  give  off  one  or 
two  dendrites  each,  which  penetrate  through  the  inner  nuclear  layer 
into  the  inner  molecular  layer, 

3.  The  inner  molecular  layer.  This  is  composed  of  five  strata. 
The  majority  of  the  spongioblasts  (amacrine  or  parareticular  cells) 
in  the  inner  nuclear  layer  send  their  processes  upward  into  the  inner 
molecular  layer,  in  which  some  end  in  fine  arborizations  in  the  first, 
others  in  the  second,  and  still  others  in  the  third  interstice,  separat- 
ing the  strata  of  the  inner  molecular  layer  from  one  another.  Be- 
sides these  so-called  stratum  spongioblasts,  there  are  also  others  in  the 
inner  nuclear  layer,  the  diffiLse  spongioblasts,  whose  ramifications  end 
simultaneously  in  several  or  in  all  of  the  strata  of  the  inner  molecu- 
lar layer.  Besides  the  ramifications  of  the  spongioblasts  just  men- 
tioned, autochthonous  cells  are  also  present.  These  lie  in  one  of 
the  interstices  of  the  molecular  layers,  their  ramifications  spreading 
out  in  a  horizontal  direction.  Besides  all  these  structures  the  den- 
drites of  the  cells  in  the  ganglion-cell  layer  also  ramify  throughout 
the  inner  molecular  layer. 

4.  The  ganglion  -  cell  layer.  The  cell -bodies  are  irregularly 
oval  ;  their  dendrites  extend  into  the  inner  molecular  layer,  and 
their  neuraxes  into  the  nerve-fiber  layer.  According  to  the 
manner  of  their  dendritic  termination,  the  ganglion  cells  may  be 
divided  into  three  groups  :  (i)  those  the  dendrites  of  which  ex- 
tend into  but  one  stratum  of  the  molecular  layer ;  (2)  those  the 
dendrites  of  which  extend  into  several  strata  of  the  molecular  layer  ; 
and  (3)  those  the  dendrites  of  which  are  distributed  throughout  the 
entire  thickness  of  the  molecular  layer.  Thus,  these  three  groups 
are  made  up  of  the  so-called  mono-stratified,  poly-stratified,  and 
diffuse  cells  ;  by  means  of  their  dendrites  they  come  in  contact  with 
one  or  several  of  the  neuraxes  of  the  bipolar  cells  of  the  inner 
nuclear  layer. 

5.  The  nerve -fiber  layer  o'i  the  retina.  This  layer  consists  of 
centripetal  neuraxes  from  the  ganglion  cells  of  the  ganglion-cell 
layer,  and  of  centrifugal  nerve -fibers  ending  in  various  layers  of 
the  retina,  including  the  outer  molecular  layer. 


8.  THE  OPTIC  NERVE. 

Within  the  orbit  the  optic  nerve  possesses  an  external  sheath, 
which  is  an  extension  of  the  dura  mater  and  is  continuous  with  the 
scleral  tissue,  and  an  inner  sheath,  which  is  a  prolongation  of  the  pia 


THE  INTERNAL  OR  NERVOUS  TUNIC  OF  THE  EYE. 


465 


mater.  Between  these  two  sheaths  is  a  fissure,  divided  into  two 
smaller  clefts  by  a  continuation  of  the  arachnoid.  Both  these  clefts 
are  traversed  by  connective-tissue  trabeculae.  The  inner  cleft  com- 
municates with  the  subarachnoid  space  ;  and  the  outer  narrower 
cleft,  with  the  subdural  space. 

The  fibers  of  the  optic  nerve  are  medullated,  but  they  possess  no 
neurilemma.  They  are  grouped  into  small  bundles  by  septa  and 
bands  of  fibrous  tissue  penetrating  the  optic  nerve  from  the  inner  or 
pial  sheath.  Within  these  bundles  the  nerves  are  separated  by  neu- 
roglia tissue, — neuroglia  cells  and  fibers, — which  further  forms  a 
thin  sheath  about  each  bundle.  In  the  region  of  the  sclera  and  cho- 
roid the  optic  nerve-fibers  lose  their  myelin,  and  the  septa  of  the  inner 
or  pial  sheath  become  better  developed  and  relatively  more  numer- 
ous. Connective-tissue  fibers  from  the  sclera  and  choroid  also  trav- 
erse this  region  of  the  optic  nerve,  giving  rise  to  what  is  known  as 
the  lamina  cribrosa.  At  from  ij4  to  2  cm.  from  the  eyeball  there 
enter  into  the  optic  nerve  laterally  and  ventrally  (according  to  J.  Deyl, 
mesially)  the  central  artery  and  vein  of  the  retina,  which  very  soon 
come  to  lie  within  the  axis  of  the  nerve.  Here  they  are  surrounded 
by  a  common  connective-tissue  sheath  which  is  in  direct  connection 
with  the  pial  sheath.  The  optic  nerve-fibers  extend  through  the 
lamina  cribrosa  into  the  retina,  where  they  spread  out  as  the  nerve- 
fiber  layer  in  the  manner  previously  described. 


-.  Vein. 


9.  BLOOD-VESSELS  OF  THE  OPTIC  NERVE  AND  RETINA. 

The  blood-vessels  of  the  optic  nerve  are  principally  derived  from 
the  vessels  of  the  pial  sheath.  In  that  portion  of  the  nerve  con- 
taining the  central  vessels  of  the 
retina  the  latter  anastomose  with 
the  pial  vessels,  so  that  this  por- 
tion of  the  optic  nerve  is  also 
supplied  by  the  central  vessels. 
At  their  entrance  through  the 
sclera  the  short  posterior  ciliary 
arteries  form  a  plexus  around  the 
optic  nerve,  the  arterial  circle  of 
Zinn,  which  communicates,  on 
the  one  hand,  with  the  vessels  of 
the  pial  sheath,  and,  on  the  other, 
with  those  of  the  optic  nerve. 
At  the  level  of  the  choroid  the 
vessels  of  the  latter  communicate 
by  means  of  capillaries  with  the 
central  vessels  of  the  optic  nerve. 

The  central  artery  and  vein 
of  the    retina    enter    and    leave 
the    retina    at    the    optic    papilla, 
30 


Fig.  362. — Injected  blood-vessels  of 
the  human  retina ;  surface  preparation ; 
Xi8. 

dividing    here,   or    even    within 


466  THE    EYE. 

the  nerve  itself,  into  the  superior  and  inferior  papillary  artery  and 
vein.  Both  the  latter  again  divide  into  two  branches,  the  nasal 
and  temporal  arteriole  and  venule,  known,  according  to  their  posi- 
tions, as  the  superior  and  inferior  nasal  and  temporal  artery  and 
vein. 

Besides  these  vessels,  two  small  arteries  also  arise  from  the 
trunk  of  the  central  artery  itself,  and  extend  to  the  macula.  Two 
similar  vessels  extend  toward  the  nasal  side  as  the  superior  and 
inferior  median  branches.  Within  the  retina  itself  the  larger  ves- 
sels spread  out  in  the  nerve-fiber  layer,  forming  there  a  coarsely 
meshed  capillary  network  connected  by  numerous  branches  with  a 
finer  and  more   closely   meshed    network    lying  within   the  inner 


Vascular 
plexus  of 
macula  lutea 
with  wide 
meshes. 

Fovea  centra- 
lis, free  from 
vessels. 


Fig-  363. — Injected  blood-vessels  of  human  macula  lutea  ;  surface  preparation  ;  X  28. 

nuclear  layer.  The  venous  capillaries  of  this  network  return  as 
small  venous  branches  to  the  nerve-fiber  layer,  in  which  they  form 
a  venous  plexus,  side  by  side  with  the  arterial  plexus. 

The  arteries  of  the  retina  are  of  smaller  caliber  than  the  veins. 
The  larger  arteries  possess  a  muscular  layer ;  the  smaller,  only  an 
adventitia.  All  the  vessels  possess  highly  developed  perivascular 
sheaths.  The  visual-cell  layer  is  nonvascular,  as  are  also  the  fovea 
centralis  and  the  rudimentary  retinal  layers  lying  anterior  to  the 
ora  serrata. 

The  arteries  of  the  retina  anastomose  with  one  another  solely  by 
means  of  capillaries  (end -arteries),  and  it  is  only  in  the  ora  serrata 
that  coarser  venous  anastomoses  exist. 


THE    CRYSTALLINE    LENS.  4^7 


F.  THE  VITREOUS  BODY. 


The  vitreous  body  is  a  tissue  which  consists  almost  entirely  of 
fluid,  containing  very  few  fixed  cellular  elements  and  only  a  small 
number  of  leucocytes,  which  are  found  more  particularly  in  its  outer- 
most portion.  Thin  structureless  lamellae  and  fibers  occur  through- 
out the  entire  vitreous  body,  with  the  exception  of  the  hyaloid  canal. 
These  fibrils  form  an  interlacing  network  with  wide  meshes.  They 
differ  chemically  from  both  the  white  fibrous  tissue  and  yellow  elastic 
fibers,  resembling  in  some  respects  cuticular  formations  (von  Ebner). 
These  are  particularly  numerous  at  the  periphery  and  especially  in 
the  reo-ion  of  the  ciliary  body.  Toward  the  surface  the  fibrils  are 
more  densely  arranged,  forming  the  hyaloid  membrane  of  the  vit- 
reous body,  separating  the  latter  from  the  retina.  This  membrane 
is  somewhat  thicker  in  the  region  of  its  close  attachment  around  the 
physiologic  excavation  of  the  optic  nerve  and  to  the  internal  limiting 
membrane  of  the  retina  in  the  ciliary  region.  In  the  latter  region 
the  hyaloid  membrane  is  in  close  relation  with  the  epithelium  of  the 
pars  ciliaris  retinae.  It  does  not,  however,  penetrate  into  and  between 
the  ciliary  processes,  but  extends  like  a  bridge  over  the  furrows  be- 
tween them..  This  arrangement  gives  rise  to  spaces,  the  recessus  cam- 
ercB  postcrioris,  which  form  a  division  of  the  posterior  chamber,  and 
are  inclosed  between  the  hyaloid  membrane,  the  ciliary  processes, 
the  suspensory  ligament  of  the  lens,  and  the  lens  itself;  these  spaces 
are  filled  with  aqueous  humor.  In  the  region  of  the  ciliary  pro- 
cesses the  hyaloid  membrane  is  closely  associated  with  numerous 
fibers,  which  diverge  fan-like  toward  the  lens  and  become  blended 
with  the  outer  lamella  of  the  lens-capsule.  These  fibers  appear  to 
arise  from  the  epithelium  of  the  pars  ciliaris  retinae,  and  may  be 
regarded  as  cuticular  formations.  Those  coming  from  the  free  ends 
of^he  ciliary  processes  become  attached  along  the  equator  of  the  lens 
and  to  the'  adjacent  posterior  portion  of  the  lens-capsule.  On  the 
other  hand,  the  fibers  originating  between  the  ciliary  processes  attach 
themselves  to  the  anterior  surface  of  the  lens-capsule  in  the  imme- 
diate vicinity  of  the  equator.  Together  these  fibers  constitute  the 
zonula  ciliaris,  zonule  of  Zinn,  or  the  suspensory  ligament  of  the  lens. 
Between  these  fibers  of  the  zonula  and  the  lens  itself  there  is,  conse- 
quently, a  circular  canal  divided  by  septa,  the  canal  of  Petit,  which 
communicates  by  openings  with  the  anterior  chamber. 

G.  THE  CRYSTALLINE  LENS. 

As  we  have  already  seen,  the  crystalline  lens  originates  as  an 
ectodermic  invagination,  which  then  frees  itself  from  the  remaining 
ectoderm  in  the  shape  of  a  vesicle  and  becomes  transformed  into 
the  finished  lens.  In  this  process  the  cells  of  the  inner  wall  of  the 
vesicle  become  the  lens-fibers,  while  those  of  the  outer  portion  re- 


468  THE    EYE. 

main  as  the  anterior  epithelium  of  the  lens.  The  lens  is  surrounded 
on  all  sides  by  the  lens-capsule. 

The  lens  capsule  is  a  homogeneous  membrane,  nearly  twice  as 
thick  on  the  anterior  surface  of  the  lens  as  on  the  posterior.  Its 
chemic  reactions  differ  from  those  of  connective  tissue,  and  in  this 
respect  it  may  be  compared  with  the  membranae  proprise  of 
glands.  In  sections  the  lens  capsule  appears  to  possess  a  tangen- 
tial striation  ;  under  the  influence  of  certain  reagents,  and  under 
proper  preliminaiy  treatment,  lamellae  may  be  detached  from  its 
surface  which  are  found  to  be  directly  connected  with  the  fibers 
of  the  suspensory  ligament. 

The  anterior  epithelium  consists,  in  the  fetus,  of  columnar  cells  •, 
in  children,  of  cells  approaching  the  cubic  type  ;  and  in  the  adult,  of 
decidedly  flattened  cells.  Toward  the  equator  of  the  lens,  in  the 
so-called  transitional  zone,  the  cells  increase  in  height  and  gradually 
pass  over  into  the  lens  fibers. 

The  lens  fibers  are  also  derivatives  of  epithelial  cells  ;  they  are 
long,  flattened,  hexagonal  prisms,  which  extend  through  the  entire 
thickness  of  the  lens.  In  the  adult  the  lens  may  be  differentiated 
into  a  resistant  peripheral  and  a  softer  axial  substance.  The  sur- 
faces of  the  fibers  present  irregularities,  and  it  is  with  the  help  of 
these  serrations  and  a  cement  substance  that  the  fibers  are  bound 
together.  Each  fiber  possesses  one  or  more  nuclei,  which,  although 
they  have  no  constant  position,  are  usually  found  in  the  middle  of 
the  fibers  situated  near  the  lens-axis,  and  in  the  anterior  third  of 
those  at  some  distance  from  the  axis.  The  course  of  the  fibers  in 
the  lens  is  extremely  complicated. 


H.  THE  FETAL  BLOOD-VESSELS  OF  THE  EYE. 

In  the  eye  of  the  embryo  the  vitreous  body  and  the  capsule  of 
the  lens  contain  blood-vessels.  The  vessel  which  later  becomes 
the  central  artery  of  the  retina  passes  through  the  space  sub- 
sequently occupied  by  the  vitreous  body  as  far  as  the  posterior  sur- 
face of  the  lens  (anterior  hyaloid  artery)  and  branches  in  the  region 
of  the  posterior  and  anterior  lens-capsule.  The  anterior  vascular 
membrane  of  the  lens  capsule  of  the  embryo  is  known  as  the 
membrana  capsulopupillajHs,  and  that  portion  corresponding  to  the 
pupil,  as  the  inembrana  pupillaris.  In  the  embryo  numerous  other 
vessels  arise  at  the  papilla  and  extend  over  the  surface  of  the 
vitreous  body  close  to  the  hyaloid  membrane  ;  these  are  the  pos- 
terior hyaloid  arteries.  These  vessels  later  disappear.  In  place  of 
the  anterior  hyaloid  artery  there  remains  in  the  vitreous  humor  a 
transparent  cylindric  cord  containing  no  fibers  nor  lamellae,  as  is  the 
case  in  the  remaining  portion  of  the  vitreous  body,  and  consisting 
of  a  more  fluid  substance  ;  this  is  the  hyaloid  canal,  or  the  canal  of 
Cloquet.  X 


THE  PROTECTIVE  ORGANS  OF  THE  EYE.  469 

With  regard  to  the  posterior  hyaloid  vessels,  the  generally  ac- 
cepted theory  is  that  they  later  enter  into  the  formation  of  the 
retinal  vessels.  Little  is  known  as  to  the  details  of  this  process  ; 
but  the  fact  remains  that,  in  the  rabbit,  for  instance,  the  larger 
branches  of  the  retinal  vessels  are  internal  to  the  inner  limiting 
membrane,  and,  therefore,  within  the  vitreous  body,  and  that  they 
send  smaller  branches  into  the  retina  (His,  80). 


L  INTERCHANGE  OF  FLUIDS  IN  THE  EYEBALL. 

The  anterior  lymph-cliannels  of  the  eye  comprise  (i)  the 
lymph-canaliculi  of  the  cornea,  which  communicate  with  similar 
structures  in  the  sclera  ;  (2)  the  system  of  the  anterior  chamber, 
which  is  indirectly  connected,  on  the  one  hand,  with  the  canal  of 
Schlemm  by  means  of  the  spaces  of  Fontana,  and  with  the  stroma 
iridis,  into  which  the  ligamentum  pectinatum  extends  ;  while,  on  the 
other  hand,  it  communicates  with  the  posterior  chamber  and  its 
recesses,  and  with  the  canal  of  Petit. 

In  the  posterior  region  of  the  eyeball  are  the  lymph-channels 
of  the  retina  (the  perivascular  spaces),  those  of  the  optic  nerve,  the 
space  between  the  pigment  layer  and  the  remaining  portion  of  the 
retina  (interlaminar  space,  Rauber),  and  the  lymph-spaces  of  the 
choroid  and  sclera.  The  influx  and  efflux  of  intraocular  fluid 
occur  principally  by  means  of  filtration.  The  influx  takes  place 
through  the  ciliary  processes  ;  that  the  choroid  has  to  do  with  this 
process  is  very  improbable.  The  efflux  takes  place  through  the 
veins  of  the  canal  of  Schlemm,  into  which  the  fluid  filters  through 
the  cement  lines  of  the  endothelial  lining  of  the  canal  of  Schlemm, 
finally  emptying  into  the  anterior  ciliary  veins.  A  posterior  efflux 
from  the  vitreous  body  probably  does  not  exist,  or  at  least  occurs 
to  a  very  limited  extent.  The  anterior  chamber  possesses  no  efferent 
lymph-vessels  (Leber,  95). 


J.  THE  PROTECTIVE  ORGANS  OF  THE  EYK 

J.  THE  LIDS  AND  THE  CONJUNCTIVA. 

At  the  end  of  the  second  month  of  embryonic  life  the  eyelids 
begin  to  develop  in  the  shape  of  two  folds  of  skin.  At  the  end 
of  the  third  month  these  folds  come  in  contact  in  the  region  of 
what  is  later  the  palpebral  fissure,  and  grow  together  at  their  outer 
epithelial  margins.  Shortly  before  birth  the  two  lids  again  separate 
and  the  definitive  palpebral  fissure  is  formed. 

The  eyelids  show  three  distinct  layers:  (i)  the  external  cutis, 
which  presents  special  structures  at  its  free  margin  and  continues 
about  I  mm.  inward  from  the  inner  border  of  the  free  margin  ;  (2) 
the  mucous   membrane,  or   palpebral   conjunctiva,  beginning   from 


470  THE    EYE. 

this  line  and  covering  the  entire  internal  surface ;  and  (3)  a  middle 
layer. 

1 .  The  cuticular  portion  of  the  eyehd  consists  of  a  thin  epider- 
mis and  a  dermis  poorly  supplied  with  papillae.  Fine  lanugo-like  hairs 
with  small  sebaceous  glands  and  a  few  sweat-glands  are  distributed 
over  its  entire  surface.  The  cutaneous  connective  tissue  is  very 
loose,  contains  very  few  elastic  fibers,  and  is  supplied  with  pigment 
cells  in  the  superficial  layers.  At  the  lid-margin  the  papillae  are 
well  developed  and  the  epidermis  is  somewhat  thickened.  The 
anterior  margin  supports  several  rows  of  larger  hairs,  the  cilia,  the 
posterior  row  of  which  possesses,  besides  the  sebaceous  glands, 
modified  sweat-glands,  the  ciliary  glands  of  Moll,  which  also  empty 
into  or  near  the  hair  follicles.  The  ciliary  glands  are  readily  distin- 
guished from  the  sweat  glands  ;  their  tubules  are  relatively  large, 
often  showing  alternating  large  vesicular  segments  and  short  narrow 
segments.  A  branching  of  the  tubules  has  also  been  observed 
(Huber).  The  eyelids  are  further  provided  with  numerous  glands, 
known  as  the  Meibomian  or  tarsal  glands.  About  thirty  of  these 
glands  are  found  in  the  upper,  a  slightly  smaller  number  in  the  lower, 
lids.  They  lie  within  the  tissue  of  the  tarsus  vertical  to  the  palpebral 
margin.  Each  gland  consists  of  a  tubular  duct,  lined  by  stratified 
squamous  epithelium,  beset  with  numerous  simple  or  branched  al- 
veoli lined  by  a  stratified,  cubic  epithelium  in  every  respect  similar  to 
that  lining  the  alveoli  of  sebaceous  glands.  The  ducts  of  these 
glands  terminate  at  the  palpebral  margin  posterior  to  the  cilia.  (See 
Fig.  364.) 

2.  The  conjunctival  portion  of  the  eyelids  is  lined  by  a  simple 
pseudostratified  columnar  epithelium,  possessing  two  strata  of  nuclei. 
This  is  continuous  with  the  bulbar  conjunctiva  at  the  conjunctival 
fornix,  and  is  characterized  by  the  occasional  presence  of  folds  and 
sulci.  Longitudinal  folds  in  the  upper  portion  of  the  upper  lid 
running  parallel  with  the  lid-margin  are  frequently  present.  Goblet 
cells  are  usually  found  in  the  epithelium.  According  to  W.  Pfitz- 
ner  (97),  the  epithelium  of  the  conjunctiva  consists  of  two  or  three 
strata  of  cells,  of  which  the  more  superficial  possess  a  cuticular 
margin.  Certain  structures  which  have  always  been  regarded  as 
goblet  cells  are  in  all  probability  similar  to  the  cells  of  Ley  dig — i.  e., 
mucous  cells,  which  do  not  pour  their  secretion  out  over  the  sur- 
face of  the  epithelium.  Some  lymphoid  tissue  is  always  found  in 
the  stratum  proprium  of  the  mucous  membrane,  and  occasionally  it 
is  seen  to  form  true  lymph-nodules.  It  is  of  some  interest  to  note 
that  a  marked  production  of  these  lymph-nodules  occurs  in  certain 
diseases.  Such  lymph-nodules  are  usually  associated  with  epithe- 
lial crypts,  which  fact  led  Henle  to  regard  them  as  glandular  forma- 
tions. Small  glands  with  a  structure  similar  to  that  of  the  lacrimal 
glands  are  also  present  in  the  palpebral  conjunctiva  ;  they  are  known 
as  accessory  lacrimal  glands  and  are  fpund  in  the  upper  eyelid,  at  the 
outer  angle  of  the  conjunctival  fornix.  Similar  glands  occur  also  at 
the  mesial  angfle  of  the  fornix. 


THE  PROTECTIVE  ORGANS  OF  THE  EYE. 


471 


3.  Besides  the  tarsals  (fibrocartilage)  the  middle  layer  of  the  eye- 
lid contains  :  (i)  The  musculus  orbicularis  oculi,  which  lies  beneath 


^'g-  3^4- — Vertical  section  of  the  upper  eyelid  of  man;  X  ^4=  '^^.  arterial  arcus  tar- 
seus  ;  c,  cilia  ;  dgt,  excreton,-  duct  of  Meibomian  gland  ;  glc,  ciliary  gland  (Moll)  ;  McR, 
ciliary  muscle  of  Riolani;  Mop,  m.  orbicularis  palpebrarum;  Mt,  n'onstriated  muscle-fibers 
of  the  tarsal  muscle  and  tendon  of  the  levator  palpebrae  superioris  ;  nlc,  Ij-mph-node  of 
the  conjunctiva  palpebras  ;    T,  tarsus  (Sobotta,  "Atlas  and  Epitome  of  Histology."). 

the  subcutaneous  tissue.      At  the   margin  of  the  lid  this  structure 
gives  off  the  musculus  ciliaris  Riolani,  which  is  composed  of  two 


472 


THE    EYE. 


fasciculi  separated  by  the  tarsus.  (2)  The  connective  tissue  be- 
tween the  bundles  of  the  musculus  orbicularis  oculi.  (3)  The  con- 
nective tissue  lying  behind  the  latter  and  the  tarsus.  In  the  upper 
lid  the  connective  tissue  mentioned  under  2  and  3  is  connected  with 
the  tendon  of  the  musculus  palpebralis  superior.  The  latter  is 
composed  of  smooth  muscle-fibers,  and  is  regarded  as  a  continua- 
tion of  the  middle  portion  of  the  striated,  voluntary  musculus  leva- 
tor palpebrae  superioris.     The  middle  layer  of  the  lower  lid  isstruc- 


b- 


H>  ■ 


Fig.   365. — Meibomian  or  tarsal  gland,  reconstructed  after  Born's  wax-plate  method; 

X20. 


turally  analogous,  except  that  here  a  fibrous  expansion  from  the 
sheath  of  the  inferior  rectus  muscle  takes  the  place  of  the  levator 
palpebrae. 


THE  PROTECTIVE  ORGANS  OF  THE  EYE.  473 

The  blood-vessels  of  the  e}''elid  lie  directly  in  front  of  the  tarsus, 
and  from  this  region  supply  adjacent  parts  ;  they  reach  the  poste- 
rior portion  of  the  lid  either  by  penetrating  the  tarsus  or  by  encir- 
cling it  (Waldeyer,  74).  The  lymph-vessels  form  a  plexus  in  front 
and  one  behind  the  tarsus. 

The  "  third  eyelid,"  the  plica  semilunaris,  contains,  when  well 
developed,  a  small  plate  of  hyaline  cartilage. 

At  the  fornix  the  epithelium  of  the  palpebral  conjunctiva  be- 
comes continuous  with  the  two-  or  three-layered  squamous  epithe- 
lium of  the  conjunctiva  bulbi.  Beneath  this  epithelium  is  found  a 
loose  fibro-elastic  connective  tissue,  presenting  subepithelial  papillae, 
and  quite  vascular.  In  it  are  found  medullated  nerve-fibers,  some 
of  which  terminate  in  free  sensory  nerve-endings  in  the  conjunctival 
epithelium  ;  others  terminate,  especially  near  the  corneal  margin,  in 
end-bulbs  of  Krause ;  and  still  others  may  be  traced  to  the  cornea, 
to  terminate  in  a  manner  previously  described. 

2.  THE  LACRIMAL  APPARATUS. 

The  lacrimal  apparatus  consists  of  the  lacrimal  glands,  their  ex- 
cretory ducts,  the  lacrimal  puncta  and  canaliculi,  the  lacrimal  sac, 
and  the  nasal  duct. 

The  lacrimal  gland,  which  is  a  branched  tubular  gland,  is  sepa- 
rated into  two  portions,  of  which  the  one  lies  laterally  against  the 
orbit  and  the  other  close  to  the  upper  lateral  portion  of  the  superior 
conjunctival  fornix.  The  structure  of  the  gland  is,  on  the  whole, 
that  of  a  serous  gland  (parotid),  with  the  difference  that  the  intralob- 
ular ducts  are  not  lined  by  a  striated  epithelium  such  as  is  found  in 
the  salivary  tubules,  and  that  those  cells  which  are  wedged  in  between 
the  secretory  elements  and  functionate  as  sustentacular  cells  (basket- 
cells)  are  here  much  more  highly  developed. 

The  excretory  ducts  of  the  orbital  division  generally  pass  by  the 
conjunctival  half  of  the  gland,  taking  up  a  few  ducts  from  the  latter 
as  they  go,  and  finally  empty  on  the  surface  of  the  conjunctiva. 
Aside  from  these,  the  lateral  portion  of  the  gland  possesses  also 
independent  ducts.  All  the  excretory  ducts  are  lined  by  columnar 
epithelium  and  surrounded  by  a  relatively  thick  connective-tissue 
wall  having  inner  longitudinal  and  outer  circular  fibers.  From  the 
lateral  portion  of  the  conjunctival  culdesac,  into  which  the  secre- 
tion is  brought  by  the  excretory  ducts  of  the  lacrimal  gland,  the 
secretion  passes  into  the  capillary  space  of  the  sac,  and  is  then 
evenly  distributed  by  means  of  the  sulci  and  papillae  over  the  con- 
junctival surface  of  the  lid.  In  this  manner  the  secretion  reaches 
the  mesial  angle  of  the  lid,  whence  it  passes  through  the  lacrimal 
puncta  into  the  lacrimal  canals. 

The  nerve  supply  of  the  lacrimal  glands  is  from  the  sym- 
pathetic nervous  system.  The  neuraxes  of  s}'mpathetic  neurones 
accompany  the  gland  ducts  and  form  plexuses  about  the  alveoli, 
the  terminal  branches  of  which  may  be  traced  to  the  gland  cells. 


474  THE    EYE. 

The  lacrimal  canals  are  lined  by  stratified  squamous  epi- 
thelium, and  possess  a  basement  membrane  as  well  as  a  con- 
nective-tissue layer  containing  circularly  disposed  elastic  elements. 
Externally  we  find  a  layer  of  transversely  striated  muscle-fibers. 

The  lacrimal  sac  is  provided  with  a  simple  pseudostratified 
columnar  epithelium  having  two  strata  of  nuclei.  In  it  goblet  cells 
are  also  found.  The  nasal  duct  is  Hned  by  a  similar  epithelium. 
The  connective-tissue  wall  of  the  latter  and  that  of  the  lacrimal 
sac  come  in  contact  with  the  periosteum  ;  between  them  is  a  well- 
developed  vascular  plexus.  Stratified  squamous  and  ciliated  epi- 
thelium have  been  described  as  being  present  in  the  nasal  duct,  as 
well  as  mucous  glands  in  both  nasal  duct  and  lacrimal  sac.  (See 
works  of  M.  Schultze,  72  ;  Schwalbe,  87.) 


TECHNIC. 

The  eyes  of  the  larger  animals,  after  having  been  previously 
cleaned  by  removing  the  muscles  and  loose  connective  tissue,  are  placed 
in  the  fixing  fluid  and  cut  into  two  equal  parts  by  means  of  an  equa- 
torial incision.     Smaller  eyes  with  thin  walls  may  be  fixed  whole. 

Müller' s  fluid,  nitric  acid,  and  Flemming's  fluid  are  usually  employed 
as  fixing  agents.  After  fixing  in  one  of  these  fluids,  different  parts  of  the 
eyeball  are  imbedded  in  celloidin  or  celloidin-parafiin  and  then  sectioned. 

The  corneal  epithelium  is  best  macerated  in  33%  alcohol ;  the 
membrane  of  Descemet  may  be  impregnated  with  silver.  In  order  to 
bring  the  fibers  of  the  latter  into  view,  Nuel  recommends  an  injection  of 
I  %  to  2  ^  formic  acid  into  the  anterior  chamber  of  the  eye  of  a  dove  or 
a  rabbit,  after  having  drawn  off  the  aqueous  humor.  The  cornea  is  then 
cut  out,  and  fixed  for  from  three  to  five  minutes  in  osmic  acid. 

The  substantia  propria  is  examined  either  by  means  of  sections 
or  by  means  of  teased  preparations  from  a  cornea  macerated  in  lime- 
water  or  potassium  permanganate.  The  sections  are  stained  with  picro- 
carmin  (Ranvier).  The  corneal  spaces  and  canaliculi  may  be  demon- 
strated in  two  ways  with  the  aid  of  silver  nitrate  ;  either  the  fresh  cornea 
of  a  small  animal  is  stripped  of  its  epithelium,  cauterized  with  a  solid 
stick  of  silver  nitrate,  and  then  examined  in  water,  in  which  case  the 
corneal  spaces  and  their  canaliculi  show  light  upon  a  dark  ground  (neg- 
ative impregnation)  ;  or  the  corneae  of  larger  animals  are  treated  in  the 
same  manner,  after  which  tangential  sections  are  made  with  a  razor,  and 
placed  in  water  for  a  few  days  ;  in  this  case  the  corneal  spaces  and  their 
canaliculi  show  dark  upon  a  light  ground  (positive  impregnation,  Ran- 
vier, 89). 

By  means  of  Altmann 's  oil  method  casts  of  the  corneal  spaces 
and  their  canaliculi  may  be  made.  Treatment  by  the  gold  method  often 
brings  out  not  only  the  nerves,  but  also  the  corneal  corpuscles  and  their 
processes. 

Ranvier  (89)  especially  recommends  a  1%  solution  of  the 
double  chlorid  of  gold  and  potassium  for  the  corneal  nerves.  The  cor- 
nea of  the  frog  is  treated  for  five  minutes  with  lemon-juice,  then  for  a 
quarter  of  an  hour  with  i  %  potassium-gold  chlorid  solution,  and,  finally, 
for  one  or  two  days  with  water  weakly  acidulated  with  acetic  acid  (2 


TECHNIC.  475 

drops  to  30  c.c.  of  water),  the  whole  process  taking  place  in  the  light. 
Golgi's  method  may  also  be  used,  but  the  gold  method  is  more  certain. 

The  sclera  is  treated  in  a  similar  manner. 

The  pigmentation  of  the  vascular  layer  interferes  with  examina- 
tion, and  albinotic  animals  should  therefore  be  selected  ;  or  the  pigment 
may  be  removed  from  the  previously  fixed  eyeball  with  hydrogen  peroxid 
or  nascent  chlorin.  The  latter  method  is  applied  exactly  as  in  cases  where 
the  removal  of  osmic  acid  is  desired. 

The  adult  lens  is  sectioned  with  difficulty,  as  it  becomes  very 
hard  in  all  fixing  fluids.  The  anterior  capsule  of  the  lens  may  be  removed 
from  previously  fixed  specimens  and  examined  by  itself.  The  lens-fibers 
are  demonstrated  by  maceration  in  ^  alcohol  (twenty-four  hours)  or  in 
strong  nitric  acid.  Before  immersion  the  lens-capsule  is  opened  by  a 
puncture. 

The  retina  can  rarely  be  kept  unwrinkled  in  eyes  that  have  been 
fixed  whole.  The  eyeball  should  therefore  be  opened  in  the  fixing  fluid 
and  the  latter  permitted  to  act  internally  ;  or  the  external  tunics  are 
removed,  thereby  enabling  the  fixing  fluid  to  act  externally. 

Ranvier  recommends  subjecting  the  eyes  of  smaller  animals 
(mouse,  triton)  for  a  quarter  or  half  hour  to  the  action  of  osmic  acid 
fumes  (see  p.  24),  after  which  the  eyes  are  opened  in  yi  alcohol  with 
the  scissors.  At  the  end  of  three  or  four  hours  the  posterior  half  of  the 
eye  is  stained  for  some  time  in  picrocarmin  (p.  44),  then  carried  over 
into  1%  osmic  acid  for  twelve  hours,  washed  with  water,  treated  with 
alcohol,  and  cut. 

In  osmic  acid  preparations  the  rod-nuclei  show  dark  transverse  bands, 
a  condition  due  to  the  fact  that  the  end-regions  of  the  nuclei  stain  more 
deeply. 

The  retina  is  a  good  object  for  differential  staining,  as,  for  instance, 
with  hematoxylin-eosin,  hematoxylin -orange  G,  etc.  The  latter  combina- 
tion is  particularly  successful  in  staining  the  rod-  and  cone -ellipsoids. 
The  examination  of  tangential  sections  should  not  be  omitted. 

With  the  retina  the  best  results  are  obtained  by  means  of  Golgi's 
method.  Attention  must  be  called  to  the  fact  that  the  supporting  struc- 
tures of  the  retina  are  more  easily  impregnated  than  the  nervous  elements, 
and  that  the  latter  can  be  demonstrated  to  any  extent  only  in  very  young 
eyes. 

Ramon  y  Cajal  (94)  recommends  the  following  method,  modi- 
fied after  Golgi :  After  the  removal  of  the  vitreous  humor  the  posterior 
half  of  the  eyeball  is  placed  for  one  or  two  days  in  a  mixture  containing 
2,%  potassium  bichromate  20  c.c.  and  i^  osmic  acid  5  or  6  c.c.  The 
pieces  are  then  dried  with  tissue  paper  and  placed  in  a  0.75^  silver 
nitrate  solution  for  an  equal  length  of  time.  Without  washing,  the  pieces 
are  immersed  for  from  twenty-four  to  thirty-six  hours  in  a  mixture  con- 
taining 3^  potassium  bichromate  20  c.c,  and  I'fc  osmicacid  2  or  3  c.c, 
and  then  again  carried  over  into  a  0.751^  silver  nitrate  solution  for 
twenty-four  hours.  In  order  to  prevent  precipitation  it  is  advisable  to 
roll  up  the  retina  before  treating,  and  to  cover  it  with  a  thin  layer  of  a 
thin  celloidin  solution,  which  prevents  it  from  again  unrolling. 

The  methylene-blue  method  (p.  184)  will  also  bring  out  the 
nervous  elements  of  the  retina,  although  the  results  are  not  quite  so  satis- 
factory as  those  obtained  by  Golgi's  method. 


476  THE    ORGAN    OF    HEARING. 


IX.  THE  ORGAN  OF  HEARING. 

The  ear,  the  organ  of  hearing,  consists  of  three  parts  :  (i)  The 
external  ear,  including  the  pinna  or  auricle  and  the  external  audi- 
tory canal ;  (2)  the  middle  ear,  tympanum,  or  tympanic  cavity, 
containing  the  small  ear  bones  and  separated  from  the  external 
auditory  canal  by  the  tympanic  membrane,  but  communicating  with 
the  pharynx  by  means  of  the  Eustachian  tube ;  (3)  the  inner  ear, 
or  labyrinth,  consisting  of  a  bony  and  a  membranous  portion,  the 
latter  lined  by  epithelial  cells,  especially  differentiated  in  certain 
regions  to  form  a  neuro-epithelium,  in  which  the  auditory  nerves 
terminate.  The  first  two  parts  serve  for  the  collection  and  trans- 
mission of  the  sound-waves  ;  the  complicated  labyrinth,  with  its 
differentiated  neuro-epithelium,  for  the  perception  of  the  same. 
Figure  366  presents  in  a  schematic  way  the  relationships  of  the 
parts  here  mentioned. 


A.  THE  EXTERNAL  EAR. 

The  cartilage  of  the  ear,  including  that  of  the  external  auditory 
passage,  is  of  the  elastic  variety,  but  differs  from  typical  elastic  carti- 
lage in  that  it  contains  areas  entirely  free  from  elastic  fibers.  The 
elastic  reticulum  is,  however,  never  absent  near  the  perichondrium. 
The  skin  covering  the  pinna  is  thin,  and  in  it  are  found  hairs  with 
relatively  large  sebaceous  glands ;  sweat-glands  are  found  on  the 
outer  surface. 

The  skin  lining  the  cartilaginous  portion  of  the  external  auditory 
canal  is  somewhat  mobile  and  possesses  very  few  pronounced 
papilljE,  and  is  characterized  by  the  presence  of  so-called  ceruminous 
glands,  which  represent  modified  and  very  highly  differentiated 
sweat-glands.  They  are  branched,  tubulo-alveolar  glands  (Huber). 
They  empty  either  into  the  hair  follicles  near  the  surface  of  the  skin 
or  on  to  the  surface  of  the  skin  in  the  neighborhood  of  the  hair  fol- 
licles. 

The  skin  lining  the  osseous  portion  of  the  external  auditory 
canal  is  supplied  with  neither  hair  nor  glands,  and  possesses  slender 
papillae,  especially  in  the  neighborhood  of  the  tympanic  membrane. 
The  corium  is  closely  attached  to  the  periosteum. 

The  tympanic  membrane  consists  of  a  tense  and  a  flaccid  portion. 
It  forms  a  part  of  both  the  external  and  the  middle  ear.  From 
without  inward,  the  following  layers  may  be  differentiated  :  (i)  the 
cutaneous  layer ;  (2)  the  lamina  propria ;  and  (3)  the  mucous  layer. 

The  epidermis  of  the  cutaneous  layer  is  identical  in  structure 
with  that  of  the  outer  skin,  except  that  the  superficial  layers  of  the 
stratum  corneum  contain  nucleated  cells.  The  corium  is  very  thin, 
except  along  the  course  of  the  manubrium  of  the  malleus,  where  it 


THE    EXTERNAL    EAR. 


477 


is  thickened,  forming  the  so-called  cuticidar  ridge,  which  possesses 
papillae  and  is  supplied  with  vessels  and  nerves. 

The  lamina  propria  ends  peripherally  in  a  thickened  ring  of  fibro- 
elastic  tissue,  the  annulus  fibrosus,  which  unites  at  the  sulcus  tym- 
panicus  with  the  periosteum  of  the  latter.  The  lamina  propria  is 
composed  of  connective -tissue  fibers,  in  which  two  layers  may  be 
distinguished — externally,  the  radiate  fibers,  the  stratum  radiattim, 
and  internally,  the  circular  fibers,  the  stratum  circidare.  The  exter- 
nal radiate  layer  extends  from  the  annulus  to  the  umbo  and  manu- 
brium, and  is   interrupted  in  the  flaccid  portion  of  the  tympanic 


Pinna 


Fig.  366. — Schematic  representation  of  the  complete  auditory  apparatus  (Schwalbe) 


membrane  by  the  upper  fourth  of  the  manubrium  and  the  short 
process  of  the  malleus  ;  it  gradually  thins  out  toward  the  center 
until  it  finally  disappears  in  the  vicinity  of  the  umbo.  The  fibers 
of  the  inner  (circular)  layer  are  circularly  disposed.  This  layer  is 
thickest  at  the  periphery  of  the  tympanic  membrane,  becoming 
gradually  thinner  toward  the  lower  end  of  the  manubrium,  where 
it  disappears.  Between  the  two  layers  of  the  lamina  propria  is  a 
small  quantity  of  loose  connective  tissue.  The  manubrium  of  the 
malleus  is  inclosed  within  the  tympanic  membrane.  This  is  due  to 
the  union  of  the  fibers  of  the  radial  layer  with  the  outer  strata  of 
the  manubrial  perichondrium,  the  handle  of  the  malleus  being  here 
covered  by  a  thin  layer  of  cartilage.  In  the  posterior  upper  quad- 
rant of  the  tympanic  membrane  the  two  layers  of  the  lamina  propria 


4/8  THE    ORGAN    OF    HEARING. 

intermingle,  forming  irregularly   disposed  bundles  and  trabeculae, 
the  dendritic  fibrous  structures  of  Gruber. 

The  mucous  layer  of  the  tympanic  membrane  consists  of  sim- 
ple squamous  epithelium  separated  from  the  lamina  propria  by  a 
thin  connective-tissue  layer  containing  but  few  cells.  It  likewise 
extends  over  the  handle  of  the  malleus.  In  the  flaccid  portion  of 
the  tympanic  membrane  the  lamina  propria  disappears,  so  that  in 
this  region  the  cutaneous  layer  and  the  mucous  membrane  are  in 
direct  contact. 


B.  THE  MIDDLE  EAR. 

The  middle  ear,  or  tympanum,  is  a  small  irregular  cavity,  filled 
with  air,  situated  in  the  petrous  portion  of  the  temporal  bone  be- 
tween the  bony  wall  of  the  inner  ear  and  the  tympanic  membrane, 
and  communicates  with  the  pharynx  through  the  Eustachian  tube. 
It  contains  the  small  bones  of  the  ear,  their  ligamentous  attach- 
ments, and,  in  part,  the  muscular  apparatus  moving  them. 

The  mucous  membrane  lining  the  tympanic  cavity  is  folded  over 
the  ossicles  and  ligaments  of  the  tympanum  and  is  joined  to  that  of  the 
tympanic  membrane  and  the  Eustachian  tube,  the  line  of  junction 
with  the  former  being  marked  by  the  presence  of  papilla-like  eleva- 
tions. 

The  epithelium  of  this  mucous  membrane  is  a  simple  pseudo- 
stratified  ciliated  epithelium,  having  two  strata  of  nuclei.  Cilia  are, 
however,  lacking  on  the  surface  of  the  auditory  ossicles,  on  their 
ligaments,  and  on  the  promontory  of  the  inner  wall,  as  well  as  on  the 
tympanic  membrane.  The  mucosa  of  the  mucous  membrane  is 
intimately  connected  with  the  periosteum,  and  may  now  and  then 
contain  short  isolated  alveolar  glands,  especially  in  the  neighbor- 
hood of  the  opening  of  the  Eustachian  tube. 

The  "auditory  ossicles"  are  true  bones  with  Haversian  canals 
and  lamellae  ;  with  the  exception  of  the  stapes,  they  contain  no 
marrow-cavity.  Very  distinct  perivascular  spaces  are  seen  sur- 
rounding the  vessels  in  the  canals  (Rauber).  The  malleus  articu- 
lates with  the  incus,  both  articular  surfaces  being  covered  with 
hyaline  cartilage.  Within  this  articulation  we  find  a  fibrocartilagin- 
ous meniscus,  and  at  the  summit  of  the  short  limb  of  the  incus 
another  small  cartilage  plate.  Between  the  lenticular  process  of  the 
incus  and  the  capitulum  of  the  stapes  is  another  articulation,  also 
provided  with  cartilaginous  articular  surfaces.  The  basal  plate  of 
the  stapes  is  covered  both  below  and  at  its  edges  with  cartilage,  as 
are  also  the  margins  of  the  fenestra  ovalis  (fenestra  vestibuli).  The 
basal  plate  is  held  in  place  within  the  fenestra  by  an  articulation, 
provided  with  tense  ligamentous  structures  on  the  tympanic  and 
vestibular  sides.  Between  these  the  connective  tissue  is  quite  loose. 
All  the  cartilaginous  portions  of  the  auditory  ossicles,  with  the  ex- 


THE    MIDDLE    EAR. 


479 


ception  of  the  articular  cartilages,  rest  on  the  periosteum  (Rüdin- 
ger,  70). 

T\iQ  fenestra  rotunda  (fenestra  cochleae)  is  closed  by  the  secon- 
dary or  inner  tympanic  membrane,  a  connective-tissue  membrane 
containing  vessels  and  nerves,  the  outer  wall  of  which  is  covered  by 
ciliated  epithelium,  the  inner  (the  surface  toward  the  scala  tympani) 
by  flattened  endothelial  cells. 

In  the  antrum  and  mastoid  cells,  the  mucosa  of  the  mucous 
membrane  is  immovably  fixed  to  the  periosteum.  The  epithelium 
is  of  the  simple  squamous  variety  and  is  nonciliated. 


Portion  of  Eusta- 
chian tube  free 
from  glands.        ^ 


Cartilage,  — 


Glands.  ,; 


Mucosa  of  the 
pharynx. 

Glands. 


^^Z-  367- — Cross- section  of  the  Eustachian  tube  with  its  surrounding  parts ;  X  12  (from 
a  preparation  by  Professor  Riidinger). 


The  mucous  membrane  of  the  osseous  portion  of  the  Eustachian 
tube  is  very  thin,  and  its  mucosa  is  intimately  connected  with  the 
periosteum.  Its  epithelium  is  of  the  simple  pseudostratified  ciliated 
variety,  having  two  strata  of  nuclei.  There  are  no  glands.  The 
mucous  membrane  of  the  cartilaginous  portion  of  the  Eustachian 
tube  is  thicker,  and  its  epithelium,  which  is  of  the  stratified  ciliated 
variety,  is  higher,  and  often  contains  goblet-cells.  Lymphoid  tissue 
may  be  demonstrated  in  the  mucosa  of  this  portion,  and  occasion- 
ally structures  resembling  lymph-nodules  are  found,  especially  in  the 
vicinity  of  the  pharyngeal  opening  of  the  tube.  In  the  cartilaginous 
portion  of  the,  tube  are  mucous   glands,  which    are   particularly 


48o 


THE    ORGAN    OF    HEARING. 


numerous  in  the  vicinity  of  the  pharyngeal  opening-  (Rüdinger,  72, 
2).  The  cartilage  of  the  Eustachian  tube  is  in  part  yellow  elastic, 
in  part  hyaline,  and  in  certain  portions  presents  the  appearance  of 
white  fibro-cartilage. 


C  THE  INTERNAL  EAR. 

.  The  internal  ear  consists  of  an  osseous  and  a  membranous  por- 
tion, the  osseous  and  the  membranous  labyrinths ;  the  latter  is  con- 
tained within  the  former,  and,  although  smaller,  presents  the  same 


Superior  semicircular  canal. 


Horizontal  semi- 
circular canal. 
Posterior  semi- 
circular canal. 


Ampulla. 


Bony  cochlea. 


Vestibule.        Fenestra  rotunda. 


Fig.  368. — Right  bony  labyrinth,  viewed  from  outer  side  :  The  figure  represents  the 
appearance  produced  by  removing  the  petrous  portion  of  the  temporal  bone  down  to  the 
denser  layer  immediately  surrounding  the  labyrinth  (from  Quain,  after  Sömmering). 


general  shape.    The  two  structures  are  separated  by  a  lymph-space 
containing  the  perilymph. 

In  the  bo?iy  labyrinth  we  recognize  a  central  portion  of  ovoid 
shape,  known  as  the  vestibule,  the  outer  wall  of  which  forms  the 
inner  wall  of  the  tympanum  and  presents  two  openings,  the  fenestra 
ovalis  and  the  fenestra  rotunda,  separated  by  a  ridge  known  as  the 
promontory.  This  ridge  becomes  continuous  with  the  lower  portion 
of  the  bony  cochlea,  anterior  and  mesial  to  the  vestibule  and  having 
the  shape  of  a  blunt  cone.  From  the  posterior  portion  of  the  ves- 
tibule arise  three  semicircular  canals,  known  respectively  as  the 
external  or  horizontal  semicircular  canal,  the  ajiterior  superior  vertical, 
and  the  posterior  inferior  vertical  semicircular  canals.  The  canals 
communicate  with  the  vestibule  by  means  of  five  openings,  the 
superior  contiguous  portions  of  the  anterior  and  posterior  canals 
uniting  to  form  the  canalis  communis  before  reaching  the  vestibule. 
The  three  canals  present  near  their  origin  from  the  vestibule  enlarge- 
ments known  as  the  osseous  ampullae.  The  osseous  labyrinth  is 
lined  throughout  by  a  thin  layer  of  periosteum,  covered  by  a  layer 
of  endothelial  cells. 


THE    INTERNAL    EAR. 


481 


The  membranous  labyrinth  differs  in  shape  from  the  osseous 
labyrinth  in  that,  in  place  of  the  single  chamber  (vestibule)  of  the 
latter,  the  membranous  labyrinth  presents  two  sacs,  the  utriculus 
and  the  sacculus,  united  by  a  narrow  duct,  the  utriculosaccular 

duct.  The  utriculus  is  the  larger,  and  from  it  arise  the  membran- 
ous semicircular  canals.  These  present  ampullae,  situated  within 
the  osseous  ampullae  previously  mentioned.  The  sacculus  com- 
municates with  the  cochlear  duct  by  means  of  the  canalis  reuniens 
(Hensen).  From  the  utriculosaccular  duct  arises  the  ductus 
endolymphaticus,  which  passes  through  the  aqueductus  vestibuli 
and  ends  in  a  subdural  sacats  endolymphaticus  on  the  posterior  sur- 
face of  the  petrous  portion  of  the  temporal  bone. 

In  the  membranous  labyrinth  the  nerves  are  distributed  over 
certain  areas  known  as  the  maadcB,  cristce,  and  papilla  spiralis. 


Auditor}'  nen-e 
with  its  vestibu- 
lar and  cochlear 
branches. 


cd  [fl 


Ant.  semicircular  canal. 
Ampulla. 


Cochlear  duct. 


Canalis  reuniens.  Ductus  Ampulla, 

endolymphaticus. 


Horizontal  semicir- 
cular canal. 


Fig.  369. — Membranous  labyrinth  of  the  right  ear  from  five-month  human  embryo  (from 
Schwalbe,  after  Retzius). 


There  is  a  macula  within  the  recess  of  the  utriculus,  the  macula 
acustica  utriculi ;  and  another  within  the  sacculus,  the  macula 
acustica  saccidi ;  cristae  are  present  in  the  ampullae  of  the  upper, 
posterior,  and  lateral  semicircular  canals,  the  cristce  ampullares  sup., 
post.,  et  hit.  Besides  these,  we  have  the  terminal  arborization  of 
the  acoustic  nerve  in  the  membranous  cochlea,  the  papilla  spiralis 
cocJdece,  or  the  organ  of  Corti. 


31 


482 


THE    ORGAN    OF    HEARING. 


U  UTRICULUS  AND  SACCULUS. 


Only  the  inner  wall  of  the  utriculus  is  connected  with  the  peri- 
osteum  of  the  vestibule.      In   this   region  lies  the  corresponding 


Membranous  semicircular  canal. 


,.'/__•>;_<'',// t  ^'.N    ^ , Epithelium  of  the 

t  'j'l',  ,  V  1- -'•/l\'*'..-.^i't7"'  membranous 

V.  '-   ■  r"  v-:^--   l^-'^'M  canal. 


Blood-vessel. ^  {I 


Wall  of  mem 
branous 
canal. 


Perilymphatic 
spaces. 


Blood-vessel. 

Fig.  370. — Transverse  section  through  an  osseous  and  membranous  semicircular  canal 
of  an  adult  human  being;  X  5°  (after  a  preparation  by  Dr.  Scheibe):  a,  Connective- 
tissue  strand  representing  a  remnant  of  the  embryonic  gelatinous  connective  tissue.  Such 
strands  serve  to  connect  the  membranous  canal  with  the  osseous  wall. 


macula  cribrosa,  through  which  the  nerves  penetrate  to  the  macula 
of  the  utriculus.  The  utriculus  and  sacculus  fill  only  a  part  of  the 
inner  cavity  of  the  osseous  vestibule.  Between  the  osseous  and 
membranous  portions  remains  a  space  traversed  by  anastomosing 
connective-tissue  trabeculse,  and  lined  by  endothelium,  which  also 
forms  an  investing  membrane  around  the  trabeculse.  These  trabe- 
culae  pass  on  the  one  side  into  the  periosteum  lining  the  vestibule, 
and  on  the  other,  into  the  wall  of  the  utriculus  and  sacculus.  The 
cavity  which  they  thus  traverse  represents  a  perilymphatic  space. 
(Compare  Fig.  370,  which  shows  analogous  relations  in  the  semi- 
circular canals.) 

The  wall  of  the  utriculus,  especially  its  inner  portion,  consists 
of  dense  fibrous  connective  tissue,  most  highly  developed  in  the 
region  of  the  macula  acustica.     In  the  immediate  vicinity  of  the 


THE    INTERNAL    EAR.  483 

macula  utriculi  the  epithelium  of  the  utriculus  is  high  columnar  in 
type  ;  in  the  remaining  portion  it  consists  of  a  single  layer  of  low 
columnar  cells,  with  a  distinct  basement  membrane  ;  the  epithelium 
of  the  macula  itself  is  also  high,  and  is  composed  of  two  kinds  of 
elements — of  sustentacular  elements  and  of  the  so-called  auditory 
hair-cells.  The  sits  tentacular  cells  are  tall  epithelial  cells  resting 
on  the  basement  membrane  by  means  of  their  single  or  cleft  basal 
plates.  Each  possesses  an  oval  nucleus  lying  at  or  beneath  the 
center  of  the  cell.  The  hair-cells  are  peculiar  cylindric  elements 
with  somewhat  thickened  and  rounded  bases.  One  end  extends  to 
the  surface  of  the  epithelium,  while  the  other,  which  contains  the 
nucleus,  extends  only  to  the  center  of  the  epithelial  layer.  The  free 
end  is  provided  with  a  cuticular  zone  supporting  a  number  of 
long,  stiff  hairs,  which  often  coalesce  to  form  single  threads.  On 
the^  surface  of  the  epithelium,  which  must  be  regarded  as  a 
neuro-epithelium,  are  crystals  of  calcium  carbonate,  known  as  oto- 
liths, each  of  which  incloses  a  minute  central  vacuole  (Schwalbe). 
The  otoliths  are  inclosed  in  a  homogeneous  substance,  the  otolithic 
membrane,  which  coagulates  in  a  network  of  filaments  when  sub- 
jected to  the  action  of  fixing  agents. 

The  nerve-fibers  going  to  the  macula  penetrate  the  wall,  and, 
under  the  epithelium,  undergo  dichotomous  division,  and,  after  fur- 
ther division,  form,  in  the  region  of  the  basilar  ends  of  the  auditory 
cells,  a  plexus  consisting  of  fine  ramifications,  and  embracing  the 
lower  ends  of  the  auditory  cells.  A  few  fibers  extend -still  further 
upward,  where  their  telodendria  enter  into  intimate  relations  with 
the  acoustic  cells  (v.  Lenhossek,  94,  i). 

The  structure  of  the  sacculus  is  in  every  respect  like  that  of  the 
utriculus,  and  a  further  description  of  it  is  therefore  unnecessary. 


2.  THE  SEMICIRCULAR  CANALS. 
The  membranous  semicircular  canals  are  attached  at  their  con- 
vex surfaces  to  the  periosteum  of  the  bony  canals,  which  they  only 
partly  fill,  the  remaining  cavity  being  occupied  by  an  eccentrically 
situated  perilymphatic  space  traversed  by  connective-tissue  trabeculae. 
The  walls  of  the  perilymphatic  spaces  of  the  semicircular  canals, 
like  those  surrounding  the  utriculus  and  the  sacculus,  are  lined  by 
endothelium,  which  covers,  on  the  one  hand,  the  periosteal  surface 
of  the  bony  semicircular  canals,  and,  on  the  other  hand,  the  outer 
wall  of  the  membranous  canals,  together  with  the  connective-tissue 
trabeculse.      The  connective-tissue  walls  of  the  membranous  canals 
are   structurally   similar   to  those   of  the    utriculus   and   sacculus. 
Hensen  compares  their  structure  to  that  of  the  substantia  propria 
of  the  cornea.      In  the  adult,  the  inner  layer  of  the  wall  of  the 
canals  supports  here  and  there  papillary  elevations,  which,  however, 


484 


THE    ORGAN    OF    HEARING. 


disappear   along   its    attachment   to    the   bony  semicircular   canal 
(Rüdinger,  72,  88). 

The  epithelium  lining  the  membranous  semicircular  canals  is 
simple  squamous  in  character  and  very  evenly  distributed  over  the 
entire  inner   surface,  including  the   papillae  previously  mentioned. 

On  the  concave  side  of  each  semicircu- 
lar canal  the  epithelial  cells  are  some- 
what narrower  and  higher.  This  inner 
and  higher  epithelium  (raphe),  extending 
along  the  concave  side  into  the  ampullae, 
marks  the  region  at  which  the  semicir- 
cular canals  were  constricted  off  from 
the  pocket-like  anlagen.  The  epithe- 
hum  of  the  ampullae  (Fig.  371),  with 
the  exception  of  that  in  the  region  of  the 
raphe,  is  of  the  squamous  type.  At  the 
cristae  of  the  ampullae,  however,  there  is 
found  a  neuro-epithelium  similar  to  that 
of  the  maculae.  The  cells  adjoining  both 
ends  of  the  cristae  are  high  columnar, 
and  to  these  the  squamous  epithelium 
is  joined.  The  columnar  cells  just  men- 
tioned form  the  so-called  semilunar  fold. 
Otoliths  are  also  present  upon  the  neu- 
ro-epithelium of  the  cristse.  Here  the 
structure  corresponding  to  the  otolithic 
membrane  of  the  utriculus  and  sacculus 
is  called  the  cupula.  In  preserved  spec- 
imens it  presents  th-e  appearance  'of  a 
coagulum,  showing  a  faint  striation  ;  in 
the  fresh  condition,  it  has  never  been  recognized  as  a  distinct  struc- 
ture, at  least  in  the  lower  classes  of  vertebrates. 


Fig.  371. — Part  of  a  verti- 
cal section  through  the  anterior 
ampulla,  showing  the  membran- 
ous wall,  a  portion  of  the  "crista 
acustica,"  and  the  "planum 
semilunatum"  (after  Retzius)  : 
a,  Semilunar  fold  ;  b,  crista  acus- 
tica ;  c,  nerve-fibers ;  d,  blood- 
vessels. 


3.  THE  COCHLEA. 

The  cochlea  consists  of  an  osseous  portion,  the  bony  cochlea, 
a  membranous  portion,  the  cochlear  duct,  and  two  perilymphatic 
canals.  The  bony  cochlea  consists  of  a  central  bony  axis  of  conical 
shape,  the  modiolus,  around  which  is  wound  a  spiral  bony  canal, 
having  in  man  a  little  over  two  and  one-half  turns,  the  modiolus 
forming  the  inner  wall  of  this  canal.  The  summit  of  the  cochlea, 
which  has  the  shape  of  a  blunt  cone,  is  formed  by  the  blind  end  of 
this  bony  canal,  and  is  known  as  the  cupola.  The  modiolus  further 
gives  support  to  a  spiral  plate  of  bone,  the  lamina  spiralis  ossea, 
which  extends  from  the  lower  part  of  the  modiolus,  and,  forming 
two  and  one-half  spiral  turns,  reaches  its  top,  where  it  ends  in  a 
hook-like  process,  the  hamulus.     This  bony  spiral  lamina  partly 


THE    INTERNAL    EAR.  485 

divides  the  bony  cochlear  canal  into  two  parts,  the  division  being 
completed  by  a  fibrous  tissue  membrane,  the  lamina  spiralis  mem- 
branacea,  which  extends  from  the  free  edge  of  the  osseous  spiral 
lamina  to  a  thickened  periosteal  ridge,  the  ligamentiini  spirale,  lining 
the  outer  wall  of  the  bony  cochlear  canal.  The  canal  above  the 
lamina  spiralis  (bony  and  membranous)  is  known  as  the  scala 
vestibuli,  that  below  as  the  scala  tympani.  Both  are  perilymphatic 
canals,  and  communicate  in  the  region  of  the  last  half-turn  of  the 
cochlea,  by  means  of  a  narrow  canal,  the  hcHcotrema,  partly  sur- 
rounded by  the  termination  of  the  bony  spiral  lamina,  the  hamulus. 
The  scala  vestibuli  is  in  free  communication  with  the  perilymphatic 
space  of  the  vestibule  ;  while  the  scala  tympani  communicates  with 
perivascular  spaces  surrounding  the  veins  of  the  cochlear  aqueduct, 
which  latter  empty  into  the  jugular  veins.  The  scala  tympani  ter- 
minates at  the  secondary  tympanic  membrane,  closing  the  fenestra 
rotunda. 

The  cochlear  duct,  which,  as  will  be  remembered,  communicates 
with  the  sacculus  by  means  of  the  canalis  reuniens,  is  a  long  tube 
closed  at  both  ends,  the  one  end  representing  the  vestibular  sac,  or 
ccBciini  vestibuläre,  and  the  other  the  cupolar  extremity,  or  cceciini 
cupolare,  also  known  as  the  lagena.  The  cochlear  duct  forms  about 
two  and  three-fourths  spiral  turns,  its  length  being  about  3.5  mm. 
Its  diameter  gradually  increases  from  its  lower  to  its  upper  or  distal 
extremity.  The  cochlear  duct  lies  above  the  lamina  spiralis,  and, 
in  a  section  of  the  cochlea  parallel  to  the  long  axis  of  the  modiolus, 
it  is  of  nearly  triangular  shape,  with  the  somewhat  rounded  apex 
of  the  triangle  attached  to  the  osseous  lamina  spiralis.  In  the 
cochlear  duct  we  may  distinguish  the  following  parts  :  (i)  the  outer 
wall,  which  is  intimately  connected  with  the  periosteum  of  the  bony 
cochlear  canal  ;  (2)  the  tympanal  wall,  resting  on  the  membranous 
basilar  membrane,  with  its  highly  differentiated  neuro-epithelium, 
the  spiral  organ  of  Corti ;  and  (3)  the  vestibular  wall,  bordering  on 
the  scala  vestibuli,  the  intervening  structures  forming  a  veiy  delicate 
membrane — the  vestibular  or  Rcissner's  membrane. 

From  the  account  given  thus  far,  it  may  be  seen  that  within  the 
bony  cochlear  canal  there  are  foimd  three  membranous  canals, 
running  parallel  with  one  another  and  with  the  osseous  lamina  spi- 
ralis about  which  they  are  grouped.  Two  of  these  membranous 
canals,  the  scala  vestibuli  and  the  scala  tympani,  are  perilymphatic 
spaces,  and  are  consequently  lined  by  endothelial  cells  ;  between 
them  is  found  the  cochlear  duct,  from  its  position  known  also  as 
the  scala  media,  lined  by  epithelial  cells.  These  three  membranous 
canals  retain  their  relative  position  in  their  spiral  course  about  the 
modiolus,  and,  in  a  section  through  the  cochlea  parallel  to  the  bony 
axis  of  the  modiolus,  would  be  met  with  at  each  turn,  and  at  each 
turn  present  essentially  the  same  relative  position  and  structure. 
In  figure  372,  which  is  from  a  longitudinal  section  of  the  cochlea 


486 


THE    ORGAN   OF    HEARING. 


of  a  cat,  the  general  relations  of  the  parts  are  clearly  shown.  Figure 
373  is  sketched  from  a  longitudinal  section  of  the  cochlea  of  a  guinea- 
pig,  and  shows  the  appearance  presented' by  a  section  through  one 
of  the  turns  of  the  bony  cochlear  canal  and  its  contents  as  seen  under 
higher  magnification.  We  may  now  proceed  with  a  fuller  consider- 
ation of  the  structures  mentioned. 


.^ 


~-^i«»c 


msp- 


■gnp 


Fig-  372- — Longitudinal  section  of  the  cochlea  of  a  cat  ;  X  25.  This  figure  gives  a 
general  view  of  the  cochlea.  The  cochlear  duct  is  met  with  six  times  in  the  section  :  aV, 
cochlear  duct ;  gsp,  spiral  ganglion  ;  Kn,  osseous  cochlear  wall ;  Isp,  ligamentum  spirale  ; 
msp,  membrana  spiralis;  mv,  membrana  vestibularis  or  Reissner's  membrane  ;  n,  nervus 
cochlearis ;  set,  scala  tympani;  scv,  scala  vestibuli  (Sobotta,  "Atlas  and  Epitome  of 
Histology"). 


The  lamina  spiralis  ossea  consists  of  two  bony  plates  which  in- 
close between  them  the  ramifications  of  the  cochlear  nerve.  The 
vestibular  surface  of  the  osseous  lamina  spiralis  is  covered  by  peri- 
osteum, which  is  continuous  with  a  peculiar  tissue,  known  as  limbus 
spiralis.    The  latter  begins  at  the  point  of  attachment  of  Reissner's 


THE    INTERNAL    EAR. 


487 


membrane,  extends  peripherally  (externally),  and  ends  in  two 
sharp  ridges,  of  which  the  shorter,  the  labium  vestibuläre,  projects 
into  the  inner  space  of  the  cochlear  duct  and  continues  into  the 
tectorial  membrane  ;  while  the  other  and  longer,  the  labiuvi  tym- 
panicum,  becomes  attached  to  the  wall  of  the  scala  tympani  and 
continues  into  the  basilar  membrane.  Between  the  two  ridges  is  a 
sulcus,  the  sulcus  spiralis  internus.    (Fig.  373-)     The  limbus  spiralis 


Fi2  373  —Section  through  one  of  the  turns  of  the  osseous  and  membranous  coch- 
lear ducts  of  the  cochlea  of  a  guinea-pig  ;  X  90  :  /,  Scala  vestibuli ;  m,  labium  vestibu- 
läre of  the  limbus ;  n,  sulcus  spiralis  internus  ;  o,  nerve-fibers  lying  in  the  lamina  spi- 
ralis ;  p,  ganglion  cells  ;  q,  blood-vessels ;  a,  bone  ;  b,  Reissner's  membrane  ;  Ä-  ductus 
cochlearis;  d,  Corti's  membrane;/,  prominentia  spiralis;  ^^,  organ  of  Corti ;  li,  Uga- 
mentum  spirale  ;  ?,  crista  basilaris  ;  k,  scala  tympani. 

is  a  connective-tissue  formation  in  the  region  of  the  cochlear  duct 
connected  with  the  periosteum  of  the  osseous  spiral  lamma  and 
extendino-  from  the  point  of  attachment  of  Reissner's  membrane 
to  the  labium  tympanicum.  The  tissue  of  the  limbus  spiralis  is 
dense  and  richly  cellular,  and  simulates  in  its  structure  the  sub- 
stantia propria  of  the  cornea.     A  casual  view  would  seem  to  disclose 


488  THE    ORGAN    OF    HEARING. 

a  high  columnar  epithehum,  but  upon  closer  observation,  it  is  seen 
that  the  cellular  elements  are  interspersed  with  fibers  which  extend 
to  the  surface.  Some  investigators  regard  this  tissue  as  fibrocar- 
tilage ;  others,  again,  as  a  tissue  siii  generis,  consisting  of  epithelial 
cells  mingled  with  connective-tissue  fibers.  If  the  labium  vestibuläre 
of  the  limbus  spiralis  be  examined  from  the  vestibular  surface,  a 
number  of  irregular  tubercles  are  seen  at  its  inner  portion  (near 
Reissner's  membrane),  while  at  its  outer  portion  long,  radially  dis- 
posed ridges  may  be  observed,  the  so-called  auditory  teeth  of 
Huschke.  The  connective-tissue  wall  of  the  sulcus  spiralis  internus 
consists  of  a  nonnucleated  fibrillar  tissue  which  is  continued  into  the 
labium  tympanicum.  The  latter  is  perforated  by  nerves,  thus  giving 
rise  at  this  point  to  the  foramina  nervosa. 

Between  the  point  of  attachment  of  Reissner's  membrane  and 
the  labium  vestibuläre,  the  superficial  epithelium  of  the  limbus  spiralis 
is  flat,  and  lines  the  auditory  teeth  and  the  depressions  between 
them  in  a  continuous  layer.  The  epithelium  of  the  sulcus  spiralis 
internus  is  somewhat  higher. 

The  ligamentum  Spirale  forms  the  thickened  periosteum  of  the 
outer  wall  of  the  osseous  cochlear  canal.  It  presents  two  inwardly 
projecting  ridges,  the  crista  basilaris,  to  which  the  membranous 
lamina  spiralis  is  attached,  and  ih.Q  prominentia  spii^alis,  which  con- 
tains one  or  several  blood-vessels ;  between  the  two  ridges  lies  the 
sulcus  spiralis  externus.  The  portion  of  the  ligamentum  spirale 
forming  the  periosteum  of  the  bony  cochlear  canal  consists  of  a 
fibrous  tissue  containing  many  nuclei,  but  changes  internally  into 
a  looser  connective  tissue.  The  connective  tissue  lying  external  to 
the  outer  wall  of  the  cochlear  duct  is  Very  dense  and  rich  in  cellular 
elements  and  blood-vessels,  but  in  the  crista  basilaris  it  changes  to 
a  hyaline,  noncellular  tissue,  continuous  with  the  lamina  basilaris. 
That  portion  of  the  spiral  ligament  lying  between  the  prominentia 
spiralis  and  the  attachment  of  Reissner's  membrane  is  known  as 
the  stria  vascularis.  The  epithelium  covering  this  area  (a  portion  of 
the  epithelium  lining  the  cochlear  duct)  consists  of  columnar,  darkly 
granulated  cells,  which  now  and  then  are  arranged  so  as  to  present 
the  appearance  of  a  stratified  epithelium,  but  which  is  more  correctly 
interpreted  as  an  epithelium  of  the  pseudostratified  variety.  This 
epithelium  shows  no  distinct  demarcation  from  the  underlying  con- 
nective tissue.  Beneath  this  epithelium  there  is  found  a  rich  capil- 
lary network,  certain  loops  of  which  extend  into  the  epithelium 
(Retzius).  It  is  thought  that  the  stria  vascularis  is  concerned  in 
the  formation  of  the  endolymph  of  the  cochlear  duct. 

The  membranous  lamina  spiralis,  or  the  basilar  membrane, 
extends  from  the  tympanic  lip  of  the  osseous  spiral  lamina  to  the 
crista  basilaris  of  the  ligamentum  spirale. 

As  already  stated,  the  tissue  composing  the  labium  tympani- 
cum of  the  limbus  extends  into   the   basilar  membrane.      In  this 


THE    INTERNAL    EAR.  489 

membrane  the  surface  toward  the  cochlear  duct  is  known  as  the 
cochlear  surface,  that  toward  the  scala  tympani  as  the  tympanic 
surface.  Two  layers  are  differentiated  in  the  basilar  membrane, 
the  lamina  basilaris  propria  and  the  tympanic  investing  layer.  The 
lamina  propria  consists,  in  turn,  of  (i)  radially  arranged  basilar 
fibers,  or  acoustic  strings  ;  (2)  two  thin  strata  of  a  homogeneous 
substance,  one  above  and  the  other  below  the  layer  of  basilar  fibers, 
the  upper  of  which  is  the  thicker  and  nucleated  ;  and  (3)  a  fine  cuti- 
cula,  of  epithelial  origin,  lying  on  the  cochlear  side.  The  tympanic 
investing  layer  is  highly  developed  in  youth,  but  later  becomes 
thinner,  and  may  then  be  differentiated  into  a  connective-tissue 
layer,  regarded  as  a  periosteal  continuation  of  the  tympanic  por- 
tion of  the  osseous  lamina  spiralis,  and  an  endothelial  cell  layer 
belonging  to  the  lining  of  the  perilymphatic  space  or  the  scala 
tympani.  In  the  vicinity  of  the  labium  tympanicum  is  a  blood- 
vessel situated  within  the  tympanic  investing  layer  of  the  basilar 
membrane — the  vas  spirale. 

Reissner's  membrane  consists  of  an  exceedingly  thin  connective- 
tissue  lamella,  lined  on  the  side  of  the  cochlear  duct  by  a  layer  of 
flattened  epithelial  cells  and  on  the  vestibular  side  by  a  layer  of 
endothelial  cells.  The  epithelium  lining  the  cochlear  duct  is  occa- 
sionally raised  into  small  villus-like  projections. 

The  Organ  of  Corti. — In  the  region  of  the  labium  tympan- 
icum of  the  limbus  spiralis  and  in  the  greater  portion  of  the 
adjoining  basilar  membrane,  the  epithelium  of  the  cochlear  duct  is 
peculiarly  modified,  forming  here  a  neuro-epithelium,  which  receives 
the  terminal  ramifications  of  the  cochlear  nerve  and  is  known  as  the 
spiral  organ  of  Corti. 

Passing  from  the  labium  tympanicum  to  the  ligamentum  spirale, 
the  following  three  regions  may  be  recognized  in  the  organ  of 
Corti  :  An  inner  region,  composed  of  the  inner  sustentacular  cells 
and  the  inner  auditory  cells  ;  a  middle  region,  consisting  of  the 
arches  of  Corti ;  and  an  outer  region,  in  which  are  found  the  outer 
auditory  cells  and  the  outer  sustentacular  cells  or  Deiters's  cells. 
Two  cuticular  membranes  are  in  close  relationship  to  the  organ  of 
Corti :  namely,  the  lamina  reticnlaris  and  the  membrana  tectoria,  or 
membrane  of  Corti. 

In  figure  374,  a  sketch  of  the  organ  of  Corti  and  adjacent 
structures,  it  may  be  observed  that  the  epithelium  lining  the  sulcus 
spiralis  internus  (at  the  right  of  the  figure)  is  of  the  pavement 
variety,  and  that  the  epithelium  becomes  gradually  thicker  until  the 
organ  of  Corti  is  reached,  where  it  becomes  suddenly  elevated  in 
the  form  of  a  wall.  In  this,  two  varieties  of  cells  are  distinguished 
— sustentacular  cells  and  inner  auditory  cells.  The  sustentacular 
cells,  which  follow  the  flattened  cells,  become  gradually  higher 
from  within  outward  and  occupy  three  or  four  rows.  Next  come 
the  inner  auditory  cells,  cylindric  elements,  somewhat  rounded  and 


490  THE    ORGAN    OF    HEARING. 

thickened  at  their  nucleated  basilar  ends.  The  latter  do  not  extend 
to  the  basilar  membrane  but  end  at  about  the  level  of  the  center  of 
the  inner  pillars.  At  the  free  end  of  each  cell  is  an  elliptic  cuti- 
cular  zone,  somewhat  broader  than  the  end-surface  of  the  corre- 
sponding cell.  In  man  about  twenty  rigid  filaments,  known  as 
auditory  hairs,  are  found  resting  on  each  elliptic  cuticular  zone. 
These  are  either  arranged  in  a  straight  row  or  they  describe  a  slight 
curve. 

The  middle  division  of  the  organ  of  Corti,  the  arches  of  Corti, 
consists  of  long  slender  structures,  known  as  pillar  cells,  or,  briefly, 
pillars,  resting  firmly  upon  the  basilar  membrane  and  forming  an 
arch  at  the  vestibular  side  of  the  latter.      They  surround,  by  the 


7. 


o  & 


/  d       =00 


Fig.  374. — Organ  of  Corti  :  At  x  the  tectorial  membrane  is  raised ;  c,  outer  sus- 
tentacular  cells  ;  d,  outer  auditory  cells  ;  /,  outer  pillar  cells  ;  g,  tectorial  membrane  ;  h, 
inner  sustentacular  cells  ;  z,/,  epithelium  of  the  sulcus  spiralis  internus  ;  k,  labium  ves- 
tibuläre ;  e,  tympanic  investing  layer  ;  w,  outer  auditory  cells  ;  n,  n,  nerve-fibers  vsrhich 
extend  through  the  tunnel  of  Corti ;  0,  inner  pillar  cell ;  q,  nerve-fibers  ;  b,  b,  basilar  meni- 
brane  ;  a,  epithelium  of  the  sulcus  spiralis  externus  ;  r,  cells  of  Hensen  ;  s,  inner  audi- 
tory cell  ;  /,  ligamentum  spirale  (after  Retzius) . 

union  of  their  free  ends,  a  space  which,  as  seen  in  figure  374. 
appears  triangular  in  section.     This  is  the  tunnel  of  Corti. 

According  to  their  position,  we  distinguish  inner  and  outer 
pillars,  the  inner  being  more  numerous  than  the  outer.  Including 
the  entire  extent  of  the  lamina  spiralis  membranacea,  we  find  that 
there  are  about  6000  of  the  inner  and  4500  of  the  outer  pillar 
cells. 

Each  pillar  cell  originates  from  an  epithelial  cell,  and  is  found 
to  be  composed  of  a  protoplasmic  portion  containing  the  nucleus, 
which  may  be  regarded  as  a  remnant  of  the  primitive  cell,  and  of  a 
cuticular  formation  derived  from  the  primitive  cell,  forming  the 
elongated  body  of  the  pillar  cell — the  pillar.  The  free  adjoining 
ends  are  called  the  heads  of  the  pillars.  The  head  of  the  inner 
pillar  is  provided  with  a  flattened  process,  the  head-plate,  which 
extends  outward  and  forms  an  obtuse  angle  with  the  axis  of  the 
pillar.     Under  this  plate,  and  at  the  outer  side  of  the  head  of  the 


THE    INTERNAL    EAR.  49  ^ 

inner  pillar,  is  a  depression  into  which  fits  the  head  of  the  outer 
pillar.  The  latter  also  extends  outward  in  the  shape  of  a  phalan- 
geal plate,  with  a  thinner  process,  the  phalangeal  process,  at  its  end. 
The  phalangeal  plate  and  process  lie  under  the  head-plate  of  the 
inner  pillar,  the  process  extending  a  little  beyond  this,  forming  an 
acute  angle  with  the  head  of  the  outer  pillar.  At  the  inner  side 
of  the  head  of  the  outer  pillar  is  a  convex  articular  surface,  with 
which,  as  a  rule,  two,  and  occasionally  even  three,  articular  sur- 
faces  of  the  inner  pillars  come  in  contact.  The  outer  and  inner 
pillars  appear  to  possess  an  indistinct  longitudinal  striation,  and 
their  basilar  plates  are  continuous  with  the  extremely  fine  cuticula 
covering  the  basilar  membrane.  The  inner  margins  of  the  basilar 
plates  belonging  to  the  inner  pillars  border  on  the  foramina  ner- 
vosa ;  while  the  outer  margins  of  the  basilar  plates  belonging  to 
the  outer  pillars  come  in  contact  with  the  basal  end  of  the  inner- 
most row  of  the  cells  of  Deiters  in  the  outer  region  of  Corti's 
organ.  The  protoplasmic  portions  of  the  pillar  cells,  constituting 
what  are  known  as  basal  cells,  lie  against  the  basilar  plates  of  the 
corresponding  pillars, — /.  e.,  on  the  basilar  membrane, — and  partly 
cover  the  bodies  of  the  pillars,  especially  the  surfaces  toward  the 
tunnel. 

In  order  to  comprehend  the  relative  position  of  the  inner  audi- 
tory cells  to  the  inner  pillars,  it  may  be  stated  that  one  auditory 
cell  rests  upon  every  two  inner  pillars. 

The  outer  region  of  Corti's  organ  is  joined  directly  to  the  outer 
pillar  cells,  and  consists  of  four  rows  of  auditory  cells  alternating 
with  an  equal  number  of  sustentacular  cells  or  Deiters's  cells. 
Following  these  structures  and  in  contact  with  them  are  the  outer- 
most sustentacular  cells,  known  as  Hensen's  cells. 

The  outer  auditory  cells  have  a  structure  similar  to  that  of  the 
inner  auditory  cells,  but  possess  a  more  slender  body.  They  do 
not  extend  as  far  as  the  basilar  membrane,  but  end  at  a  distance 
from  the  latter  equal  to  about  double  their  own  length.  The  cutic- 
ular  zone  of  each  outer  auditory  cell  likewise  assumes  the  form  of 
an  ellipse,  with  its  long  axis  pointing  radially.  The  surface  of  this 
zone  also  is  provided  with  about  twenty  stiff  auditory  hairs, 
arranged  in  the  form  of  a  decidedly  convex  arch,  the  convexity  of 
which  points  outward.  At  a  short  distance  from  the  cuticular  zone 
of  each  outer  auditory  cell  is  a  peculiar  round  body,  found  only  in 
these  cells,  the  significance  of  which  is  unknown. 

Deiters's  cells  rest  on  the  basilar  membrane,  and  in  shape  resem- 
ble a  flask  with  a  narrow  neck,  known  as  the  phalangeal  p7'ocess, 
the  latter  lying  between  the  auditory  cells.  The  nuclei  of  Deiters's 
cells  lie  in  the  upper  parts  of  the  thickened  basal  portions  of  these 
cells. 

With  each  Deiters's  cell  there  is  associated  a  cuticular  structure, 
which  extends  along  the  surface  of  each  cell  in  the  form  of  a  thin 


492  THE    ORGAN    OF    HEARING. 

fiber,  the  sustentacular  fiber,  and  which  is  found  partly  within  and 
partly  without  the  cell.  The  sustentacular  fiber  begins  near  the 
center  of  the  thicker  basal  portion  of  the  cell-body  and  extends  first 
into  the  cell  itself,  then  passes  to  the  surface,  and,  entering  the 
phalangeal  process,  passes  to  the  top  of  the  cell  and  expands  as  a 
plate,  to  which  the  name  phalangeal  plate  has  been  given.  The 
latter  is  broader  than  the  phalangeal  process,  and  since,  as  we  shall 
see,  the  phalangeal  plates  are  joined  to  one  another,  as  well  as  to 
the  elliptically  shaped  cuticular  zones  of  the  outer  auditory  cells, 
there  remains  a  space  between  the  cells  of  Deiters  and  the  auditory 
cells,  as  also  between  the  outer  pillars  and  the  innermost  of  the 
outer  auditory  cells,  known  as  Nuel's  space.  To  the  basal  regions 
of  the  inner  row  of  the  cells  of  Deiters  is  joined  the  basal  plate  of 
the  outer  pillars  of  the  arches  of  Corti. 

Next  to  the  outer  row  of  Deiters's  cells  are  the  cells  of  Hensen, 
arranged  in  about  eight  radially  disposed  rows.  They  form  an 
eminence  which  is  high  internally,  but  gradually  decreases  in  height 
externally.  The  somewhat  narrowed  bases  of  Hensen's  cells  prob- 
ably extend,  without  exception,  to  the  basilar  membrane.  The  free 
surfaces  of  these  cells  are  likewise  covered  by  a  thin  cuticular  mem- 
brane, in  man  the  cells  of  Hensen  usually  contain  yellow  pigment ; 
in  the  guinea-pig,  as  a  rule,  fat ;  and  in  the  rabbit,  generally  rudi- 
ments of  sustentacular  fibers.  Externally  the  cells  of  Hensen  graduv 
ally  change  into  elements  of  a  more  cuboid  type — the  cells  of 
Claudius,  of  which  there  are  about  ten  rows,  radially  disposed.  The 
surfaces  of  the  latter  also  possess  a  cuticular  margin  ;  the  nucleus  is 
at  the  center  of  each  cell  and  pigment  is  also  present.  Darker 
elements  with  more  basally  situated  nuclei  sometimes  occur  be- 
tween these  cells,  giving  rise  to  the  appearance  of  a  double-layered 
epithelium  (Bottcher's  cells). 

Thus  far  we  have  considered  in  detail  the  cells  comprising  the 
organ  of  Corti,  and  described  their  relative  positions  and  sequence 
from  within  outward.  In  order  to  give  a  clearer  understanding  of 
the  mutual  relations  of  these  cells,  from  Avithin  outward  and  in  the 
direction  of  the  spiral  turning  of  the  cochlea,  we  shall  now  consider 
the  appearance  presented  in  a  surface  view  of  the  organ  of  Corti. 

From  within  outward  a  surface  view  of  the  organ  of  Corti  pre- 
sents the  following  characteristics  :  The  somewhat  broadened  hex- 
agonal outlines  of  the  inner  sustentacular  cells  adjoin  the  epithelial 
elements  of  the  sulcus  spiralis  internus  and  terminate  externally  in 
a  spiral  undulating  line  (if  seen  for  only  a  short  distance,  this  line 
appears  straight).  On  this  line  border  the  contours  of  the  cuticular 
zones  belonging  to  the  inner  auditoiy  cells.  The  outer  margins  of 
the  cuticular  zones  come  in  contact  with  the  head-plates  of  the 
inner  pillars,  the  cuticular  zone  of  one  inner  auditory  cell  coming  in 
contact  with  at  least  two  head-plates.  The  externally  directed  pro- 
cesses of  the  head-plates  belonging  to  the  inner  pillars  come  in 
contact  with  one  another  and  end  in  a  spiral  line  which  for  a  short 


THE    INTERNAL    EAR. 


493 


vY-d^^^ 


distance  is  apparently  straight.  The  head-plates  of  the  inner  pillars 
cover  the  head-plates  of  the  outer  pillars  (which  also  come  in  con- 
tact with  each  other),  also  their  phalangeal  plates,  but  not  their 
phalangeal  processes,  which  thus  pro- 
ject beyond  the  line  formed  by  the 
outer  borders  of  the  head-plates  of 
the  inner  pillars.  It  should  be  men- 
tioned that  about  three  head-plates 
belonging  to  the  inner  pillar  cells  are 
in  apposition  to  every  two  head-plates 
and  their  phalangeal  processes  of  the 
outer  pillar  cells.  The  succeeding 
four  rows,  from  within  outward,  are 
made  up  of  alternately  placed  cutic- 
ular  zones  of  the  outer  hair  cells  and 
the  phalangeal  plates  of  the  Deiters's 
cells,  alternating  like  the  squares  of  a 
chess-board.  This  regular  arrange- 
ment is  lost  in  the  outer  row  of 
Deiters's  cells.  The  cells  of  Hensen 
adjoin  this  row,  and  when  viewed  from 
the  surface,  present  the  appearance  of 
irregular  polygons. 

This  arrangement  is,  however,  sel- 
dom found  to  be  as  typical  as  that 
just  described  ;  although  the  relations 
of  the  cells  to  one  another  always 
correspond  in  general  to  the  forego- 
ing scherne. 

In  the  cupolar  and  vestibular  sacs 
the  neuro-epithelium  changes  into  an 
epithelium  of  an  indifferent  type. 

The  lamina  reticularis  is  formed 
by  the  cementing  together  of  the  pha- 
langeal processes  of  the  outer  pillars 
and  the  phalangeal  plates  of  Deiters's 
cells,  and  is  continued  externally  by  a 
cuticular  membrane  which  covers  the 
cells  of  Hensen  and,  as  a  much  thin- 
ner cuticular  membrane,  extends  over 
the  cells  of  Claudius.  In  this  mem- 
brane there  are  found  three  or  four 
rows  of  small  apertures,  into  which 
the  outer  hair  cells  project. 

The  membrana  tectoria  Cortii  is 
attached   to   the   limbus   spiralis,    but 
becomes  free  at  the  margin  of  the  labium  vestibuläre  and  thick' 
ens   considerably,    again    becoming    thinner    toward    its    free    end 


Fig.  375- — Surface  of  the  organ 
of  Corti,  with  the  surrounding  struc- 
tures, from  the  basal  turn  of  the 
cochlea  of  a  new-born  child  ;  the 
original  drawing  reduced  one-half 
(after  Retzius,  84):  tf,  Epithelium 
of  the  sulcus  spiralis  externus ;  b, 
Hensen' s  cells;  c,  terminal  frame; 
d,  phalanges  ;  f,  outer  auditory  cells; 
g,  flattened  processes  of  the  outer  pil- 
lar cells  ;  h,  flattened  processes  of  the 
inner  pillar  cells  ;  ?',  inner  auditory 
cells  ;  k,  inner  sustentacular  cells  ; 
/,  epithelium  of  the  sulcus  spiralis 
internus  ;  vi,  margin  of  the  labium 
vestibuläre ;  n,  epithelium  of  the 
limbus  laminae  spiralis  ;  o,  line  of 
attachment  of  the  membrana  Reiss- 
neri  ;  /,  epithelium  of  the  membrana 
Reissneri,  the  latter  inverted. 


494  THE    ORGAN    OF    HEARING. 

Hence  an  inner  attached  and  an  outer  free  zone  may  be  dififerentiated. 
This  membrane  has  no  nuclei,  and  shows  a  fine  radial  striation. 
Its  free  portion  bridges  over  the  sulcus  spiralis  internus  and  rests 
upon  the  organ  of  Corti.  Its  outer  margin  extends  as  far  as  the 
cells  of  Hensen.  The  development  of  this  membrane  is  not 
thoroughly  understood,  although  it  very  probably  represents  a  dis- 
placed cuticular  formation  belonging  to  the  cells  of  the  limbus 
spiralis.     This  acceptation  has  recently  been  confirmed  (Exner). 

The  auditory  nerve  gives  off,  soon  after  entering  the  internal 
auditory  meatus,  vestibular  branches  to  the  maculae  in  the  utriculus 
and  sacculus  and  to  the  cristse  in  the  semicircular  canals,  and  a 
cochlear  branch,  which  passes  up  through  the  modiolus  in  anasto- 
mosing bony  canals.  From  this  centrally  placed  column  of  nerve- 
fibers,  a  continuous  sheet  of  nerve-fibers,  arranged  in  the  form  of 
anastomosing  bundles,  passes  radially  into  the  osseous  spiral  lamina 
and  thence  to  the  organ  of  Corti.  Near  the  base  of  the  osseous 
spiral  lamina,  along  the  entire  length  of  this  sheet  of  nerve-fibers, 
there  is  situated  in  a  special  bony  canal  a  ganglion,  known  as  the 
spiral  ganglion  of  the  cochlea.  The  ganglion  cells  of  this  ganglion 
are  bipolar,  one  of  the  processes  of  each  cell,  the  dendrite,  extending 
outward  through  the  osseous  spiral  lamina  to  the  organ  of  Corti, 
the  other  process,  the  neuraxis,  passing  through  the  bony  canal  in 
the  modiolus,  through  the  internal  auditory  meatus,  and  thence  to 
the  medulla.  The  dendritic  processes  of  the  nerve-cells  of  the 
spiral  ganglion  form  bundles  of  medullated  nerve-fibers,  which  pass 
outward  within  the  osseous  spiral  lamina,  forming,  in  the  outer  por- 
tion of  the  latter,  a  closely  meshed  plexus,  from  which  small  bundles 
of  nerve-fibers  proceed  through  the  foramina  nervosa  of  the  labium 
tympanicum  to  the  organ  of  Corti  ;  immediately  before  passing 
through  these  foramina,  the  medullated  nerve-fibers  lose  their 
medullary  sheaths  and  neurilemma. 

These  nonmedullated  fibers,  with  or  without  further  dividing,  are 
then  arranged  in  small  bundles,  which,  for  a  certain  distance, 
have  a  spiral  course  :  that  is  to  say,  parallel  to  the  tunnel  of  Corti. 
One  such  spiral  bundle  is  situated  on  the  inner  side  of  the  inner 
pillars,  under  the  inner  row  of  hair  cells  ;  another,  on  the  outer  side 
of  the  inner  pillars,  in  the  tunnel  of  Corti.  Other  fibers  pass 
through  the  tunnel  of  Corti,  so-called  tunnel-fibers,  to  reach  the 
outer  side  of  the  arches  of  Corti,  where  they  are  arranged  in  three  or 
four  spiral  bundles,  at  the  outer  side  of  the  outer  pillars  and  between 
the  rows  of  the  cells  of  Deiters.  From  the  nerve-fibers  of  these 
spirally  arranged  bundles,  terminal  branches  are  given  off,  which 
terminate,  after  further  division,  on  the  inner  and  outer  hair  cells 
(Retzius,  Geberg). 

Regarding  the  blood-vessels  of  the  membranous  labyrinth,  it 
should  be  mentioned  that  the  internal  aiiditory  artery  is  a  branch  of 
the  basilar  artery,  and  divides  into  the  rami  "vestibuläres  and  rami 
cochleares.  The  branches  of  the  former  accompany  those  of  the 
auditory  nerve  as  far  as  the  utriculus  and  sacculus.     At  the  maculae 


THE    INTERNAL    EAR. 


495 


and  cristae  the  capillary  networks  are  numerous  and  finely  meshed, 
but  in  the  remaining  portions  of  the  utriculus,  sacculus,  and  semi- 
circular canals,  they  form  coarser  networks.  The  cochlear  branch 
accompanies  the  divisions  of  the  auditory  nerve  as  far  as  the  first 
spiral  turn  of  the  cochlea  ;  the  arteries  supplying  the  remaining 
turns  enter  the  axis  of  the  modiolus,  where  they  divide  into 
numerous  branches.  The  latter  are  coiled  in  a  peculiar  manner, 
forming  the  so-called  glomeruli  arteriosi  cochlecs.  From  these, 
branches  are  given  off  which  penetrate  the  vestibular  wall  of  the 
lamina  spiralis  ossea,  where  they  supply  the  limbus  spiralis  and  the 
small  quantity  of  connective  tissue  in  the  membrana  vestibularis. 
Other  branches  surround  the  scala  vestibuli,  supply  the  walls  of  the 
latter,  and  then  continue  to  the  ligamentum  spirale,  the  stria  vascu- 
laris, and  the  lamina  basilaris. 


Fig-  376. — Scheme  of  distribution  of  blood-vessels  in  labyrinth  (after  Eichler") : 
g.  Artery ;  k,  spiral  ganglion  ;  i,  vein  ;  v,  scala  vestibuli ;  Dc,  ductus  cochlearis  ;  c,  cap- 
illaries in  the  ligamentum  spirale  ;  d,  capillaries  in  the  limbus  spiralis ;  /,  scala  tympani. 


The  venous  trunks  lie  close  to  the  arteries  and  receive  their 
blood  from  the  veins  which  lie  at  the  tympanal  surface  of  the  lamina 
spiraHs  and  from  those  which  encircle  the  outer  wall  of  the  scala 
tympani.  The  former,  in  turn,  receive  their  blood  from  the  capil- 
laries of  the  limbus  spiralis  ;  the  latter,  principally  from  the  region 
of  the  ligamentum  spirale  and  the  basilar  membrane. 

From  this  description  it  is  seen  that  the  arterial  channels  are 
connected  with  the  scala  vestibuli,  the  venous  with  the  scala  tym- 
pani, and  that  the  inner  blood  stream  circulating  through  the  lamina 
spiralis  and  limbus  spiralis  is  separated  from  the  blood  current  of  the 
two  scalae,  the  ligamentum  spirale,  and  the  crista  basilaris  (Eichler). 

The  entire  membranous  labyrinth  is  filled  with  endolymph.  The 
ductus  endolymphaticus  is,  as  will  be  .remembered,  a  canal  ending 


496  THE    ORGAN    OF    HEARING. 

under  the  dura  in  a  saccus  ejtdolymphaticus.  In  connection  with 
the  latter  are  epithelial  tubules  bordering  upon  lymph-channels, 
with  which  they  probably  communicate  by  means  of  interepithelial 
(intercellular)  spaces  (Rüdinger,  88).  The  efferent  channels  for 
the  perilymph  of  the  vestibule  extend  along  the  nerve  sheaths  of 
those  nerves  supplying  the  maculae  and  cristae  ;  these  passageways 
finally  communicate  with  the  subdural  or  subarachnoid  spaces. 
The  perilymph  of  the  cochlea  is  carried  off  by  the  adventitious 
tissue  of  the  vena  aqueductus  cochleae,  the  lymph-vessels  of  which 
empty  into  certain  subperiosteal  lymph-channels  near  the  inner 
margin  of  the  jugular  fossa. 


4.  ON  THE  DEVELOPMENT  OF  THE  LABYRINTH. 

In  man  the  epithehum  lining  the  membranous  labyrinth  origi- 
nates from  the  ectoderm  as  a  single-layered  epithelial  vesicle,  the 
auditory  vesicle  or  the  otocyst,  during  the  fourth  week  of  embryonic 
life.  After  being  constricted  off  from  the  ectoderm,  this  vesicle 
lies  in  the  vicinity  of  the  epencephalon  and  is  surrounded  by  mesen- 
chyme. The  auditory  vesicle  then  develops  a  dorsomesial  evagina- 
tion,  which  gradually  grows  larger  and  finally  becomes  the  ductus 
endolymphaticus.  An  evagination  also  occurs  in  the  ventral  wall 
of  the  vesicle,  the  recessus  cochlecB.  At  the  same  time  the  mesial 
wall  is  pushed  inward,  thus  incompletely  dividing  the  vesicle  into 
two  smaller  sacs — the  dorsal  iitricidus  and  the  ventral  saccuhis. 
From  the  utricular  portion  there  arises  a  horizontal  evagination, 
flat  and  quite  broad — the  first  trace  of  the  lateral  or  horizontal 
semicircular  canal  ;  soon  after,  another  evagination,  vertical  and 
still  broader  than  the  first,  is  seen — the  anläge  of  the  other  two 
canals.  The  outer  portion  of  these  pouches  gradually  expands, 
while  in  the  middle,  the  two  layers  of  each  evagination  come  in 
contact  with  each  other  and  coalesce,  finally  becoming  absorbed. 
In  the  vertical  evagination  two  such  areas  of  adherence  are  found, 
thus  forming  a  superior  and  a  posterior  canal,  both  having  a  com- 
mon crus  at  one  end. 

The  recessus  cochleae  grows  both  in  a  longitudinal  and  in  a  spiral 
direction,  forming  the  cochlear  duct. 

In  the  immediate  vicinity  of  the  membranous  labyrinth,  the 
mesenchyme  is  differentiated  into  a  connective -tissue  wall  for  the 
former.  The  successive  layers  of  mesenchyme,  except  in  those 
areas  where  the  membranous  labyrinth  later  becomes  adherent  to 
the  osseous,  are  transformed  into  a  mucous  connective  tissue.  The 
latter  is  surrounded  by  a  more  compact  tissue,  from  which  are  de- 
rived, first,  cartilage  ;  then  bone  and  periosteum,  and  thus,  finally, 
the  osseous  labyrinth.  By  a  peculiar  process  of  regressive  meta- 
morphosis most  of  the  mucous  connective  tissue  later  disappears. 
In  the  adult  it  is  replaced  by  the  perilymphatic  spaces  of  the  laby- 
rinth. 


TECHNIC.  497 

TECHNIC. 

In  the  treatment  of  the  external  and  middle  ear  the  usual 
methods  are  employed.  For  the  study  of  the  epithelium  in  conjunction 
with  the  adjacent  bone  the  tissue  is  fixed  and  then  decalcified,  or  sub- 
jected to  those  fixing  methods  which  accomplish  both  processes  at  the 
same  time.  The  latter  method,  however,  can  be  applied  only  to  very 
small  objects. 

The  manipulation  of  the  membranous  labyrinth,  especially  that 
of  the  adult,  is  a  very  difficult  technical  problem.  Its  isolation  from  the 
petrous  portion  of  the  temporal  bone  without  injury  can  be  accomplished 
only  in  well-advanced  fetuses  and  in  children,  and  even  here  a  thorough 
knowledge  of  the  situation  of  the  parts  in  the  petrous  portion  of  the  tem- 
poral bone  is  essential.  Smaller  animals,  especially  rodents,  afford  better 
specimens.  In  the  latter,  the  semicircular  canals  and  cochlea  give  rise  to 
more  or  less  distinct  projections  into  the  tympanic  cavity.  If  the  latter 
be  opened,  the  situation  of  the  parts  may  be  ascertained  from  without.  In 
the  rabbit  and  guinea-pig,  the  entire  cochlea  projects  into  the  tympanic 
cavity,  and  may  be  easily  removed  in  toto  with  a  strong  knife,  and,  as 
the  bony  cochlea  in  these  animals  has  very  thin  walls,  it  offers  very  little 
resistance  to  the  decalcifying  fluid  (use,  for  instance,  3^  nitric  acid). 

According  to  Ranvier's  method  (89),  the  cochlea  is  opened  with 
a  scalpel  in  a  2  ^  solution  of  osmic  acid  in  normal  salt  solution.  After 
twelve  hours  the  cochlea  is  placed  for  decalcification  in  2  ^  chromic  acid, 
which  is  frequently  changed.  In  guinea-pigs,  for  instance,  decalcification 
is  accomplished  in  a  week. 

According  to  the  method  of  Retzius  (84),  the  opened  cochlea  is 
treated  for  half  an  hour  with  a  0.5%  aqueous  solution  of  osmic  acid,  and 
then  for  the  same  length  of  time  with  a  0.5%  aqueous  solution  of  gold 
chlorid.  The  organ  of  Corti  is  then  dissected  out  and  examined  as  a 
whole,  or  cut  after  carefully  removing  the  bone. 

The  labyrinth  of  the  human  adult  is  usually  prepared  as  follows  : 
The  apex  of  the  petrous  portion  of  the  temporal  bone  is  removed  and  the 
upper  semicircular  canal,  together  with  the  cochlea,  opened  in  Müller' s 
fluid  ;  in  this  solution  the  pyramid  is  left  for  three  weeks  ;  during  the  first 
week  the  fluid  is  changed  daily,  and  every  two  days  during  the  following 
weeks.  The  specimen  is  then  washed  for  twenty-four  hours  in  running 
water,  placed  in  80^  alcohol  for  two  weeks,  and  finally  in  96%  alcohol 
for  two  days.  The  preparation  is  now  ready  for  decalcification.  This  is 
done  with  51^  nitric  acid,  which  is  to  be  changed  daily  (ten  days  to  two 
weeks).  Then  follows  washing  for  two  days  in  running  water,  carrying 
over  into  80^  alcohol  for  twenty-four  hours,  then  into  96^  alcohol  for 
from  six  to  eight  days,  and,  finally,  infiltration  and  imbedding  in  cel- 
loidin  (A.  Scheibe). 

The  following  method  may  also  be  employed  with  good  results  : 
The  isolated  pyramid  with  opened  semicircular  canal  and  cochlea  is 
treated  with  Müller' s  fluid  for  two  days  at  room-temperature,  and  then 
for  three  weeks  in  a  thermostat  at  23°  C.  During  the  latter  period,  the 
fluid  should  be  changed.  The  specimen  is  then  washed  for  forty-eight 
hours  in  running  water,  treated  for  fourteen  days  with  80^  alcohol,  then 
for  eight  days  with  96%  alcohol,  decalcified,  and  further  treated  as  in 
the  preceding  method. 

32 


49S  THE    ORGAN    OF    SMELL. 

Up  to  the  present  time  it  has  been  customary  to  cut  sections  in 
celloidin  ;  but  the  combined  celloidin-parafifin  method  may  also  be  em- 
ployed with  good  results,  and  even  the  paraffin  method,  if  great  care  be 
exercised  in  imbedding  the  tissue. 

The  nerve-fibers  and  nerve-endings  of  the  cochlea  may  be 
stained  with  the  chrome-silver  method.  For  this  purpose  it  is  recom- 
mended to  employ  embryos  or  young  fetuses. 


X.  THE   ORGAN    OF   SMELL. 

The  nasal  cavity  consists  of  the  vestibule,  the  respiratory  region 
with  the  accessory  cavities,  and  the  olfactory  region. 

The  vestibule  is  lined  by  stratified  squamous  epithelium.  In 
the  region  of  the  anterior  nares  are  hairs,  the  sebaceous  glands  of 
which  are  markedly  developed,  while  at  the  level  of  the  cartilage 
mucous  glands  are  also  present.  The  stratified  squamous  epithe- 
lium ceases  at  the  anterior  end  of  the  inner  turbinate  bone  and  at 
the  inferior  nasal  duct. 

The  respiratory  region  possesses  a  simple  pseudostratified, 
ciliated  epithelium  having  two  strata  of  nuclei  and  provided  with 
goblet  cells  ;  the  direction  of  the  ciliate  movement  is  toward  the 
posterior  nares.  Numerous  leucocytes  are  usually  found  in  the 
epithelium  and  in  the  underlying  mucosa.  Branched  alveolar 
glands,  having  mucous  and  serous  alveoli,  are  here  present.  Within 
the  mucosa  are  highly  developed  vascular  plexuses,  more  especially 
of  a  venous  character.  The  accessory  cavities  are  likewise  lined 
by  cihated  epithelium,  the  ciliate  movement  being  directed  exter- 
nally. 

The  olfactory  region  is  principally  confined  to  the  superior  tur- 
binate bone  and  to  the  nasal  septum  lying  opposite,  although  in 
the  immediate  vicinity  of  the  olfactory  region  a  few  small  islands  of 
the  same  epithelial  type  are  found,  either  entirely  isolated  or  con- 
nected with  the  principal  region  by  narrow  bridges.  In  a  fresh 
condition  the  olfactory  region  may  be  differentiated  from  the  sur- 
rounding tissue  by  its  color,  which  is  distinctly  yellow  in  man. 
Its  pigment  is  contained  within  the  sustentacular  cells  described 
on  the  next  page. 

The  epithelium  of  the  olfactory  region  is  of  the  columnar  pseudo- 
stratified type,  with  several  strata  of  nuclei,  and  consequently 
closely  simulates  a  stratified  columnar  epithelium.  Here  we  dis- 
tinguish olfactory  cells  and  sustentacular  cells. 

The  olfactory  cells  occupy  a  peculiar  position  among  the  cells 
of  special  sense  in  that  they  represent  true  ganglion  cells  (Schultze, 
Golgi,  Ehrlich,  Ramon  y  Cajal).  Within  the  epithelial  layer  they 
appear  as  spindle-shaped  cells,  with  a  spheric  nucleus  provided  with 
a  large  nucleolus  lying  in  the  thickest  portion  of  each  cell.  The 
nuclei  of  the  different  cells  lie  at  varying  levels  in  the  middle  stratum 


THE    ORGAN    OF    SMELL. 


499 


of  the  epithelial  layer.  Toward  the  nasal  cavity,  the  cells  terminate 
in  blunt  cones,  upon  each  of  which  are  several  stiff  hairs,  the  olfac- 
tory hairs.  The  basilar  ends  form  true  centripetal  nerve-processes, 
neuraxes,  which  end  in  the  peculiar  telodendria  constituting  the  glo- 
meruli of  the  olfactory  bulb.      (See  p.  422.) 

The  nuclei  of  the  sustentacular  cells  are  more  oval  and  are  situ- 
ated at  nearly  the  same  level.  These  cells  present  the  appearances 
of  long  columnar  cells,  which  toward  the  basement  membrane  ter- 
minate in  one  or  several  processes.  Between  the  basilar  ends  of 
these  cells  Ave  find  a  layer  of  elements  the  broad  nucleated  bodies  of 
which  rest  on  the  basement  membrane,  while  their  upper  extremities 
terminate   in   short   superficial   processes. 

The   mucosa  contains  a  large  number  of  leucocytes  as  well  as 


'\\ 


im^^^fm^m^^^^W^^^ 


Fig-  377- — Portion  of  transverse  section  of  the  olfactory  region  of  man;  X  15°  :  A 
zone  of  olfactory  hairs  ;  ep,  epithelium  ;  2,  zone  of  oval  nuclei ;  j,  zone  of  round  nuclei ; 
^/,  olfactory  or  Bowman's  glands;  ;/,  branch  of  olfactory  nerve;  //,  mucosa  or  tunica 
propria  with  blood-vessels  (Sobotta,  "Atlas  and  Epitome  of  Histology"). 


numerous  branched  tubular  glands,  the  so-called  olfactory  glands  or 
the  glands  of  Bowman.  In  man  these  are  albuminous  (serous) 
glands,  and  their  cells  sometimes  contain  pigment. 

Jacobson 's  organ  consists  of  blindly  ending  tubes,  situated  at 
the  lower  portion  and  at  the  outer  side  of  the  nasal  septum.  It  is 
lined  by  an  olfactory  mucous  membrane  and  receives  a  branch  of  the 
nasal  nerve.      This  organ  is  rudimentary  in  man. 

The  capillaries  spread  out  immediately  beneath  the  basement 
membrane  of  the  epithelium.  In  the  submucous  connective 
tissue,  we  find  a  relatively  w^ell  developed  vascular  plexus,  rich  in 
venous  vessels  ;  this  plexus  is  especially  marked  at  the  posterior 
portion  of  the  inferior  turbinate  bone,  forming  here  a  tissue  which 
resembles  erectile  tissue. 


500  THE    ORGAN    OF    SMELL. 

A  dense  network  of  lymphatics  ramifies  throughout  the  mucous 
membrane,  carrying  the  lymph  to  the  pharynx  and  palate.  These 
lymph-vessels  may  be  injected  through  the  subarachnoid  space 
(Key  and  Retzius). 

The  nerves  (trigeminal)  are  widely  distributed  in  the  epithelium, 
ramifying  through  both  the  respiratory  and  olfactory  regions. 
After  repeated  divisions  these  nerves  lose  their  medullary  sheaths, 
and  end  in  telodendria  which  are  usually  provided  with  terminal 
nodules,  although  some  are  found  which  end  in  mere  filaments. 


TECHNIC. 

The  nasal  mucous  membrane  is  fixed  in  situ  with  osmic  acid  or 
one  of  its  mixtures,  after  which  small  pieces  are  removed.  It  should  be 
mentioned  that  the  nonmedullated  fibers  of  the  olfactory  nerve  assume  a 
brownish  color  under  this  treatment,  while  the  fibers  •  of  Remak  do  not 
(Ranvier,  89). 

In  order  to  isolate  the  epithelial  elements,  pieces  of  the  mucous 
membrane  are  treated  with  the  Yi  alcohol  of  Ranvier.  But  since  the 
prolongations  of  the  olfactory  cells  (neuraxes)  shrivel  and  curl  in  this 
fluid,  Ranvier  recommends  that,  after  the  epithelial  cells  have  been 
macerated  in  yi  alcohol  for  one  or  two  hours,  they  be  treated  with  i  % 
osmic  acid  for  a  quarter  of  an  hour.  If  shreds  be  now  placed  in  water 
and  teased,  the  cells,  together  with  their  prolongations,  may  be  isolated 
without  the  curling  of  the  latter. 

The  chrome-silver  method  applied  to  the  nasal  mucous  membrane 
of  young  animals  and  fetuses  has  been  the  means  of  establishing  the 
important  fact  that  the  olfactory  cells  of  the  olfactory  region  are  in  reality 
peripherally  situated  ganglion  cells. 


INDEX. 


Abbe's  apparatus,  19 

Absorption  of  fat  by  intestine,   288 

method  of  studying,  306 
Accessory  disc  of  Engelman,   139 

lacrimal  glands,  470 

thread  of  spermatosome,  361 
Acervulus,  423 

Acetic  acid,  effect  on  connective  tissue, 
128 
on  red  blood-corpuscles,    188 

subhmate  solution  as  fixing  fluid,    25 
Achromatic   portion   of   nucleus,    63 

spindle,  68    • 
Acidophile    granules,    technic    for,     227 
Adenoid   connective   tissue,    196 
Adipose  tissue,  107 

stain  for,  130 
Agminated  lymph-nodules,  197 
Air-cells,  314 
Air-spaces,  ultimate,  313 
Akrosome,  377 
Alcohol  as  fixing  solution,  23 

as  macerating  solution,  22 
Alcoholic  borax-carmin  solution  as  stain, 

41 
in   bulk,    46 
Alkalies,  effect  on  red  blood-corpuscles, 

189 
Altmann' s     method     of     demonstrating 
granules  in  cells,   77 
of  mounting,  78 
process,  55 
Alum-carmin  as  stain,  42 

in  bulk,  46 
Alveolar  ducts,  314,  315 
glands,   91 

compound  branched,  91 
simple,  91 
branched,  91 
periosteum,  242 
Alveoli,  88 
lung,  314 

of  mammary  gland,  epithelium  of,  401 
Amacrine  cells,  464 
Amitosis,  64,  70 
Amitotic  cell-division,  70 
Amphiaster,  68 
Amphipyrenin,  63 

Amphophile  granules,  technic  for,  228 
Ampullae  of  Thoma,  204 
Anaphases,  65,  69 
Anastomoses,  222 
Anilin  stains,  44 


Animals,  injection  of,  54 
Anisotropic  transverse  disc,  138 
Annulospiral  nerve-ending,  178 
Annulus  fibrosus,  477 

atrioventricularis,  214 
Anterior   epithelium   of   crystalline    lens 
468 

ground  bundle,  411 

hyaloid  artery,  468 

lymph-channels  of  eye,  469 

superior  vertical  canal,  480 
Anterolateral    columns,    ascending,    411 

descending,  411 
Antrum  of  ovary,  347 
Anus,  281 
Apathy's   method   for   demonstration    of 

fibrillar   elements   of   nervous   system, 

442 
Apochromatic  lens,  19 
Aponeuroses,  105 
Aqueous  borax  carmin  solutions  as  stain, 

41 

humor,  446 
Arachnoid,  437 
Arches  of  Corti,  490 
Arcuate  fibers  of  cornea,  450 
Area  cribrosa,  332 

vasculosa,  186 
Areas  of  Langerhans,  301 
Arrectores  pilorum,  393 
Arteriae  arciformes,  332 

capsulares  glomeruliferae,  334 
Arterial  circle  of  Zinn,  465 

retia  mirabilia,  333 
Arteries,  216 

coronary,   214 

hyaloid,  anterior,  468 
posterior,  468 

interlobular,  of  kidney,  332 

medium-sized,  218 

of  choroid,  455 

of  retina,  466 

precapillary,  218 
Arteriolae  rectae  spuriae,  333 

verae,  334 
Artery,  auditory,  internal,  494 

central,  of  retina,  465 

hepatic,  293 

nasal,  inferior,  of  retina,  466 
superior,  of  retina,  466 

papillary,  inferior,  of  retina,  466 
superior,  of  retina,  466 

renal,  332 


501 


502 


INDEX. 


Artery,  temporal,  inferior,  of  retina,  466 

superior,  of  retina,  466 
Ascending  anterolateral  columns,  411 
Association  fibers  of  cerebral  cortex,  420 
Astrocytes,  435 

Atresia  of  ovarian  follicles,  353 
Atria,  314 

Attraction-sphere,  62 
Auditory  artery,  internal,  494 

cells,  outer,  491 

hairs,  490 

nerve,  494 

ossicles,  478 

teeth,  488 
Auerbach's  plexus,  286 
Auriculoventricular  valves  of  heart,  213 
Axial    canals    of   small   intestine,    285 

cords,  157,  160 

fibrils    of,     demonstration     of,     181 

sheath,   176 

thread  of  spermatosome,  361 
sheath  of,  361 
Axillary  glands,  398 
Axis-cylinder,  159 

naked,   1 60 
Axis-fibrils,   157 
Axolemma,  157 


Baillarger's  striation,  421 

Balsam,   Canada,  as  mounting  medium, 

Bardeen's  table  for  drav/ing  of  portions - 

of  sections  to  be  reconstructed,  57 
Bars  of  intercellular  cement,  86 
Bartholin's  ducts,  253 

glands,  360 
Basement  membrane,  81,  88 

of  small  intestine,  278 
Basic  stains,  41 
.Basichromatin  granules,  62 
Basilar  membrane,  488 
Basket  cells,  254 
Baskets,  fiber,  of  retina,  462 
Basophile  granules,  193 

cells  with,  209 

technic  for,    228 
Bechtereff     and     Kaes'     striation,     421 
Benda's    chromatoid    accessory    nucleus, 

377 

method    for  demonstration   of  medul- 
lary sheath,  442 

selective    neuroglia    staining    method, 

445 
Berkley's  method  of  derhonstrating  nerves 

of  liver,  308 
Berlin  blue  as  injection  fluid,  55 
Bertini,  columns  of,  324,  330 
Bethe's  method  of  fixing  methylene-blue 
for  nerve-fibers,    184 
of  staining   neurofibrils  and    Golgi- 
nets,  443 
Bile  capillaries,  290,  291,  292 
demonstration  of,  306 
impregnation  of,  307 
effect  on  red  blood-corpuscles,  188 


Bile-ducts,  296 

Bioblasts,  60 

Biondi-Heidenhain  triple  stain,  46 

Bipolar  cells  of  cone-visual  cells,  463 

of  rod-visual  cells,  463 
Bismarck  brown  as  stain,  44 
Bladder,  336 
nerves  of,  339 
technic  of,  343 
Blastema,  64 

Blastodermic  layers,  primary,  79 
Elastomeres,  70,  79 
Blood,  186 

coagulation  of,  195 
Blood,  cover-glass  preparations,  227 
current,  behavior  of  blood-cells  in,  196 
demonstration    of,    through    vessels, 
231 
elements  of,  method  of  examining,  227 
films,    Wright's    method    of    staining, 

229 
formation  of,  186 
islands,  186 
plasma,  187 
platelets,  194 

fixation  of,  227 
shadows,  188 
sinus,   222 

supply  of  bronchi,  316 
of  Fallopian  tubes,  355 
of  heart,  214 
of  intestine,  283 
of  lymph-glands,  200 
of  salivary  glands,  259 
of  spleen,   203 
of  thymus  gland,  212 
of  thyroid  gland,  320 
of  uterus,  357 
technic  of,  226 
Blood-cells,  behavior  of,  in  blood  current, 
196 
counting,  232 

red,      nucleated,     containing      hemo- 
globin, 208 
staining  of,  227 
Blood-corpuscles,     cover-glass     prepara- 
tions, 226 
red,  187.     See  also  Erythrocytes. 
technic  of,  226 

white,  igi.     See  also  Leucocytes. 
Blood-coimting  apparatus,  Thoma-Zeiss, 

232 
Blood-forming  organs,  186 

technic  of,   226 
•Blood-placques,  194 
Blood-vessels,  186,  216 
fetal,   of  eye,  468 
in  striated  muscular  tissue,  143 
nerve  supply  of,  223 
of  bone-marrow,  210 
of  central  nervous  system,  439 
of  eyehd,  473 
of  kidney,  332 

of  hver,  distribution  of,  demonstration, 
306 
examination  of,  343 


INDEX. 


503 


Blood-vessels  of  lung,  316 

of  membranous  labyrinth,  494 
of  mucosa  of  large  intestine,  284 
of  pelvis  of  kidney,  338 
of  small  intestine,  284 
of  nasal  cavity,  499 
of  optic  nerve,  465 
of  ovary,  354 
of  pancreas,  302 
of  prostate,  370 
of  retina,  465 
of  sclera,  449 
of  stomach,  284 
of  suprarenal  glands,  341 
of  teeth,  242 
of  testis,  367 
Blutlymphdrüsen,   200 
Body-cell,  71 

Böhmer's  hematoxylin  as  stain  for  bulk, 
46 
hematoxylon,  42 
Bone,  112 
breakers,  120 
calcium  carbonate  in,  alkaline  purpurm 

as  stain  for,  132 
canaliculi,  113 
compact,    of    shaft,    development    of, 

124 
corpuscles,  113 

Schmorl's    method  of    staining,   133 
Virchow's  method  of  isolating,    134 
decalcification  of,  132 
fluids  used  for,  132 
V.  Ebner's  method,  133 
development  of,   116 
endochondral,   116 
intramembranous,  122 
endochondral,   116 
intracartilaginous,  116 
intramembranous,  116,  122 
lacunae  of,  X12,  113 
lamellae,   113 

composition,  114 
method  of  examining,  131 
Hme-salts  in,  hematoxylin  as  stain  for, 
132 
isolation  of,   132 
soft     and     hard     parts,     relation     of, 

method  of  studying,  132 
spaces  in,  Ranvier's  method  for  dem- 
onstrating, 132 
structure  of,    112 

undecalcified,  microscopic  preparation 
of,  131 
Bone-cells,  112,  115 
Bone-marrow,  207 
blood-vessels  of,  210 
gelatinous,  210 
red,  207 
technic  of,    234 
yellow,  207,  210 
Bony  cochlea,  484 

labyrinth,  480 
Borax-carmin,  alcoholic,  41 
in  bulk,   46 
aqueous,  41 


Bom's      method      of      construction     by 

plates,  56 
Böttcher's  cells,  491 
Boundary  zone,  choroid,  453 
Bowman's  capsule,  323 

glands,  499 

membrane,  449 
Box  for  imbedding  tissues,  28 
Bronchi,  311 

blood  supply  of,  316 

branches  of,  311 

ners'es  of,  317 

terminal  branches  of,   313 
Bronchioles,   311 

respiratory,  313 

terminal,  314,  315 
Brownian  movement  of  cells,  61 
Brticker's  Unes,    137 
Brunner's  glands,   265,   277 
Budding,   64 
Bulb  hairs,  393 
Bulbus  ocuh,  446 
Burdach's  column,  411 
Bütschh's  foam-structure,  staining  for,  79 

C^CUM   CUPOLARE,    485 

vestibuläre,  485 
Calcification   of   cartilages,    in 
Camera  lucida,   20 
Canada    balsam    as    mounting    medium, 

52 
Canalicular  system  in  cartilage,  method 

of  demonstrating,  131 
lymph,  102 
Canaiiculi  of  bone,  113 
Canahs  communis,  480 
Capillaries,   220 

bile,    290,    291,    292 
demonstration  of,  306 
impregnation  of,  307 

demonstrating  distribution  of,  235 

lymph,    224 

of    cerebellar    cortex,    440 

of    cerebral    cortex,    440 

of  sweat-glands,   397 
Capsule,  Bowman's,  323 

lens,  46S 

of  cartilage,  gold  chlorid  as  stain  for, 

131 

of  glands,  92 

of  Glisson,  289 

of  Ivmph-glands,  198 

of  Tenon,  448 

suprarenal,  demonstration  of,  343 
Carmin  as  stain,   41 

mass,  cold,  as  injection  fluid,  5J 
Carmin-bleu    de   Lyon,  45 
Carnoy's    acetic    acid-alcohol-chloroform 
mixture,   23 

acetic-alcohol    mixture,     23 
Carotid  gland,  225 
Cartilage,   108 

calcification  of,  in 

canaUcular     system     in,     method     of 
demonstrating,  131 


504 


INDEX. 


Cartilage,    capsules   of,  gold    chlorid  as 

stain  for,  131 
connective    tissue    in,    picrocarmin    as 

stain  for,  131 
corrosive  sublimate  as  fixative  for,  130 
cuneiform,  310 
elastic  fibers  in,  picrocarmin   as   stain 

for,  131 
fibro-elastic,   no 
glycogen   in,    iodo-iodid   of   potassium 

stain  to  demonstrate,  131 
ground-substance  of,  change  in,  in 
hyaKne,   108 
of  larynx,  310 
of  Wrisberg,  310 
osmic  acid  a  fixative  for,  130 
ossification  of,  in 
Caustic  potash  as  macerating  solution,  22 
Cell,  58 

absence  of  membrane,  62 
air-,  314 
amacrine,  464 
auditory,  outer,  491 
basket,  254 

blood,   behavior  of,   in  blood  current, 
196 

counting  of,  232 

red,  nucleated,  containing  hemoglo- 
bin, 208 

staining  of,  227 
body-,  71 
bone-,   112,   115 
Brownian  movement  of,   61 
centro-acinal,  300 
chief,  of  acini  of  thyroid  gland,  320 

of  hypophysis,  423 
chromophilic,  of  hypophysis,  423 
ciliated,  60 

colloid,  of  acini  of  thyroid  gland,  320 
commissural,  408 
cone-visual,  459 

bipolar  cell  of,  463 
connective-tissue,  fat  producing,  97 

fixed,   103 
cortical,    small,    of    cerebellar    cortex, 

415 
crystals  of,  61 
cuneate,  301 
definition  of,  58 
Deiter's,  491 
demilunar,   257 
diagram  of,  59 
diffuse,  of  retina,  464 
double  staining  of,  76 
enamel,   243 
endothelial,  80,  94 

and  mesothelial,  method  of  studying 
relations,  95 

demonstration  of,  95 

technic  for,  233 
epithelial,  in  small  intestine,  275 

isolated,  examination  of,  95 
fat  of,  61 

fat-,  scheme  of,  107 
fixing  of  chromic  acid  for,  75 
corrosive  sublimate  for,  75    ■ 


Cell,  Flemming's  solution  for,  75 
picric  acid  for,  75 
flagellated,  60 
folUcular,  372 
ganglion,   149 

demonstration  of,    182 
of  Dogiel,  in  spinal  ganglia,  426 
giant,   209 
glandular,   61 
glycogen  of,  61 
goblet,  87,   265 

granular,  of  cerebellar  cortex,  416 
granules    in,     Altmann's     method    of 

demonstrating,  77,  78 
hair-,  of  utriculus,  483 
hepatic,  cords  of,  290 
horizontal,  of  retina,  464 
liver-,  examination  of,  306 
glycogen  in,  demonstration  of,  306 
lutein,  353 
marrow-,  208 
mast-,   104 

granules  of,  technic  for,  228 
mesameboid,  80 
mesotheHal,  80 

and  endothehal,  method  of  studying 
relations,  95 
migratory,  103,  104,  193 
mitosis  of,  demonstration  of,  75 
mitral,  421 

of  olfactory  bulb,  421 
.    molecular  movement  of,   61 
monostratified,  of  retina,  464 
mother,   374 
mucus-secreting,  87 
muscle-,     cardiac,     demonstration    of, 
148 

nonstriated,   134 

of  fibers  of  Purkinje,  147 
nerve-,  149.     See  also  Ganglion  cell. 
neuro-epithelial,  92 
neuroghar,  434 
of  Böttcher,  492 
of  Claudius,  492 
of  column  of  Clark,  408 
of   Golgi,  408,  418,  419 
of  Hensen,  491,  492 
of  Langerhans,  300 
of  Leydig,  470 
of  Martinotti,  418,  419 
of   pancreas,    inner    and    outer   zones, 

methods  of  differentiating,  308 
of  Purkinje,   153 

of  cerebellar  cortex,  415 
of  reticular  connective  tissue,  100 
of  Sertoli,  364 
olfactory,   498 
parareticular,  464 
pigment,  61,  77,  104 
pillar,  490 

heads  of,  490 

inner,  490 

outer,  490 
plasma,   104 
plurifunicular,   408 
polarity   of,    81 


INDEX. 


50s 


Cell,  polygonal,   of  cerebral  cortex,  417 
polymorphous,  of  cerebral  cortex,  418 
polynuclear,   70 
polystratified,  of  retina,  464 
pyramidal,    large,   of    cerebral   cortex, 

417 
of  cerebral  cortex,  153 
small,  of  cerebral  cortex,  417 
rod -visual,   458 

bipolar  cell  of,  463 
seminal,  primitive,  372 
sense,  81 

sexual,  fertilization  of,  71 
male,  development  of,  72 
matured,   71 
somatic,   71 
spider,  435 

spindle-shaped,  of  cerebral  cortex,  417 
staining   of,   76 

stellate,    large,    of    cerebellar    cortex, 
416 
of  cerebellar  cortex,  415 
of  cerebral  cortex,  417 
of  liver,  295 
sustentacular,  92,  250,  372,  483 
tendon,  from  tail  of  rat,  107 
visual,  458 

wandering,  60,  103,  104 
with  basophilic  granules,   209 
with  eosinophile  granules,  209 
Cell-bodies  of  neurones,  149 
Cell-body,  59 
Cell-division,  64 
amitotic,   70 
direct,  64,  70 
indirect,  64 
karyokinetic,  heterotypic,  374 

homeotypic,  374 
mitotic,    of    fertilized    whiteiish    eggs, 
66,  67 
ten  stages  of,  65 
Cell-masses,  intertubular,  of  pancreas,  301 
Cell-microsomes,  59 
Celloidin  imbedding,  30 
diagram  for,  32 
infiltration,  30 

diagram  for,   32 
sections,  cutting  of,  with  sliding  micro- 
tome, 36 
dextrin  method  of  fixing,  40 
Celloidin-paraffin  imbedding,  32 

infiltration,  32 
Cell-plate,   70 
Cell-spaces  of   areolar  connective  tissue, 

102 
Cellular  elements   of  areolar   connective 

tissue,    103 
Cement  lines,    146 
Cementum,    241,    246 
Centers    of    ossification,    116 
Central  artery  of  retina,   465 

gray   nuclei   of  cerebellar   cortex,    416 
nervous    system,    406 

blood-vessels   of,  439 
fibrillar     elements     of,     Apath/s 
method  of  demonstrating,  442 


Central    nervous    system,    lymph-vessels 
of,  440 
membranes   of,  436 
technic  of,  440 
spindle,   68 
vein  of  retina,  465 
Centripetal  fibers  of  cerebral  cortex,  420 
Centro-acinal  cells,  300 
Centrosomes,  62,  427 
Centrospheres,  62,  427 
Cerebellar  columns,   direct,   411 
cortex,  413 

capillaries  of,  440 

central  gray  nuclei  of,  416 

granular  layer  of,  416 

granular  cells  of,  416 
large  stellate  cells  of,  416 
medullary  substance  of,  416 
climbing  fibers  of,  416 
mossy  fibers  of,,  416 
molecular  layer  of,  413 

cells  of  Purkinje  of,  415 
small  cortical  cells  of,  415 
stellate  cells  of,  415 
Cerebral  cortex,  416 
capillaries  of,  440 
medullary  substance  of,  419 
association  fibers  of,  420 
centripetal  fibers  of,  420 
commissural  fibers  of,  420 
projection  fibers  of,  419 
stellate  cells  of,  417 
molecular  layer  of,  417 

polygonal  cells  of,  417 
spindle-shaped  cells  of,  417 
polymorphous  cells  of,  418 
pyramidal  cell  of,  153 
large,  417 
small,  417 
Ceruminous  glands,  398,  476 
Cervical  canal,  islands  of  ciliated  epithe- 
lium in,  356 
Chemotaxis,  61,  276 
Chemotropism,   61 
Chief  cells  of  acini  of  thyroid  gland,  320 

of  hypophysis,  423 
Chlorate  of  potassium  and  nitric  acid  as 

macerating  solution,  23 
Chondrin,  method  of  obtaining,  112 
Choroid,  446,  452 
arteries  of,  455 
boundary  zone  of,  453 
glassy  layer  of,  452,  453 
lamina  vasculosa  Halleri  of,  452 
plexus,  439 
Choroidal  fissure,  447 
Chromatin,   63 

Chromatoid  accessory  nucleus  of  proto- 
plasm of  spermatid,  377 
Chromatolysis,   74 

technic,   74 
Chromatophile  granules,   149 
Chromic  acid  as  fixing  solution,  26 
as  macerating  solution,   22 
for  fixing  cells,   75 
Chromophilic    cells    of   hypophysis,    423 


5o6 


INDEX. 


Chromosomes,  67 

daughter,  68 
Chrzonszczewsky's    physiologic    auto-in- 
jection, 306 
Chyle-vessels,    285 
Cilia,  81,  470 

movement  of,  method  of  observing,  95 
CiUary  body,  446,  452,  453 
nerve  supply  of,  456 
glands,  398,  454 

of  Moll,  470 
muscle,  454 

meridional  division,  454 
middle  division,  454 
third  or  inner  division,  454 
processes,  453 
Ciliated  cells,   60 

epithelium,     islands     of,     in     cervical 
canal,  356 
Circulation  of  hypophysis,  424 
Circulatory  system,  212 

technic  of,   235 
Circulus  arteriosus  iridis  major,  455 

minor,   456 
Circumanal  glands,  398 

of  Gay,   282 
Circumferential  lamellae,  inner,    113 

outer,   113 
Circumvallate  papillae,  249 
Clark's  column,  408 

cells  of,  408 
Claudius,  cells  of,  492 
Clearing  fluids,   52 

Climbing  fibers  of  cerebellar  cortex,  416 
Clitoris,   360 
Cloquet's  canal,  468 
Club  hairs,  393 
Coagulation  of  blood,  195 
Coal-tar  stains,  44 
Cochlea,  484 
bony,  484 

perilymph  of,  496  • 

spiral  ganglion  of,  494 
technic  for,   297 
Cochlear  duct,  484,  485 
Cohnheim's  fields,   140 

method  of  impregnation,  48 
Coil-glands,  396 
Collective  lens,   19 

Colloid  cells  of  acini  of  thyroid  gland,  320 
Colostrum,  402 

corpuscles,  402 
Columns,  anterolateral,  ascending,  411 
descending,  411 
cerebellar,  direct,  411 
lateral,  408 

mixed,  411 
of  Bertini,   324,  330 
of  Burdach,  411 
of  Clark,  408 
cells  of,  408 
of  Goll,  411 
of  Gower,  411 
of  Sertoli,  364 
P3nramidal,  crossed,  411 
ventrolateral,  408 


Columns,  ventromesial,  408 
Columnas  rectales  Morgagni,  282 
Commissural  cells,  408 

fibers  of  cerebral  cortex,  420 
Commissures  of  spinal  cord,  412 
Compound  microscope,  17 
Concentric  lamellae,  113 
Concretions  of  prostate,  370 
Condensers,    19 
Cone-fibers  of  retina,  459 
Cone-visual  cells,  459 

bipolar  cells  of,  463 
Coni  vasculosi  Halleri,  364 
Conjunctiva,  469 

scleral,  448 
Conjunctiva]   portion  of  eyehds,   470 
Connective  tissue,  96 

action  of  acetic  acid  on,  128 
of  hydrochloric  acid  on,  128 
of  potassium  hydrate  on,   128 
adenoid,   196 
areolar,   loi 

cell-spaces  of,   102 
cellular  elements  of,    103 
ground-substance  of,    102 
matrix  of,   102 
development  of,  schematic  diagram 

of,  98 
effect  of  pepsin  on,   128 

of  trypsin  digestion  on,  127 
fibrous,   loi 
white,  99 
in  cartilage,  picrocarmin  as  stain  for, 

131 
magenta  red  as  stain  for,    128 
mucous,   100 
of  liver,  294 
orcein  as  stain  for,  128 
Ranvier's    method    for    examination 

of,   126 
reticular,   100 

cells  of,   100 
slide  digestion  of,  129 
technic  of,   126 
Connective-tissue  cells,  fat  producing,  97 
fixed,   103 
corpuscles,   103 
fibrillse  and  reticulum,  differential  stain 

for,   128 
framework     of     organs     and     tissues, 
digestion  method  for  demonstrating, 
129 
Contraction-ring,    158 
Conus  medullaris,  406 
Convoluted  tubules  of  testes,  363 
Cord,  spinal,  406     See  also  Spinal  cord 
Cords,   axial,    157,    160 

fibrils  of,  demonstration  of,  181 
hepatic,   290 
medullary,   199 
of    hepatic    cells,    290 
pulp,   204 
Corium,  379,  382 
Cornea,  446,  449 

anterior  elastic  membrane  of,  449 
arcuate  fibers  of,  450 


INDEX. 


507 


Cornea,  epithelium  of,  449 
ground  plexus  of,  4.51 
ner\"e5  of,  451 
technic,  474 
perfo raring  libers  of,  450 
posterior  elastic  membrane  of,  450 
subepithelial  plexus  of,  45 1 
substantia  propria  of,  449 

technic,  474 
superficial  plextis  of,  451 
Corneal  corpuscles,  450 
epithelium,  technic  of,  474 
spaces,  450 
technic  of,  474 
Corona  radiata.  347 
Coronar\-  arteries,  214 
Corpora  amylacea  of  prostate,  370 

lutea  spuria,  353 
Corpus  albicans,  353 
Highmori,  363 
luteum,  353 
verum,  353 
■  Corpuscles,   blood-,   red,    1S7.     See   also 
•     Erythrocytes. 

blood-,     white,     191.     See    also    Leu- 
cocytes. 
bone,   113 

Schmorl's  method  of  staining,  133 
Virchows  method  of  isolating,    134 
colostrum,  402 
connective-tissue,   103 
corneal,  450 
genital,   171 
Golgi-Mazzoni,  3SS 
Grandry's  technic  of,  405 
Hassal's,  212 
Herbst' s,   174,  389 

technic  of,  405 
Malpighian,  202,  203,  323,  324 
Meissner' s,   170 

technic  of,  405 
Pacinian,  3SS 

technic  of,  405 
tactile,  3S7 
Vater-Pacinian,   1 73 
distribution  of,   174 
Corrosive  sublimate  as  fixative  for  car- 
tilage,  130 
as  fixing  solution,  24 
for  fixing  cells,  75 
Cortex,  cerebellar,  413.     See  also  Cere- 
bellar cortex. 
cerebral,  416.     See  also  Cerebral  cortex. 
of  ovary,  344 
Cortical  cells,  small,  of  cerebellar  cortex, 

layer  of  hair,  3S9 

nodules,   19S 

substance  of  kidney,  323,  324 
Corti"s  arches,  490 

membrane,  4S9,  493 

organ,  48 i,  489 

spiral  organ,  489 
Cover-slips,  20 

fixing    of    large    number    of    paraffin 
sections  to,  39 


Cowper's  glands,  370 

Cox's  method  of  impregnation,  51 

Crescents  of  Gianuzzi,  256 

Crista  basilaris,  4S8 

Cristae,  48 1 

Crossed  pwamidal  columns,  411 

Crosses,  Ran\-ier"s,  demonstration  of,  180 

Crypts,  Lieberkuhn's,  276 

of  stomach,   266 
Crystalline  lens,  467 

anterior  epithelium  of,   468 
Crystals,  hematoidin,  231 

hemin,  method  of  obtaining,  230 

hemoglobin,     method     of     obtaining, 
230 

of  cell,  6\ 

Teichmann' s,   iSS 

method  of  obtaining,  230 
Cuneate  cells,  301 
Cuneiform  cartilages,  310 
Cup,  optic,  447 
Cupola,  4S4 
Cupula,  4S4 
Currents  of  diffusion,  29 
Cutaneous  laver  of  t^-mpanic  membrane, 

476 

epidermis  of,  476 
Cuticle,  379 
of  hair,  389 
inner,  389 
Cuticula,  62,  Si,   274 

dentis,   23S 
Cuticular  portion  of  eyelids,  470 
ridge.  477 
structures,  81 
Cutis,  379.     See  also  Skin. 
Cylindric  end-bulb  of  Krause,  172 
Czermak's  interglobular  spaces.  241 
Czocor's  cochineal  solution,   42 


Daüar  as  mounting  medium,  52 
Daughter  chromosomes,  68 

nuclei.  64 

stars.  374 
Decalcification,   132 

V.  Ebner's  method,  133 
Decalcif\"ing  fluids.   132 

aqueous  solution  of  nitric  acid,  133 
hydrochloric  acid,  132 
Deiters  cells,  491 
Delafield's  hematoxy-lin.  43 
Demilunar  cells.  257 
Demilunes  of  Heidenhain,  256 
Dendrites,   149,   150 

function  of,   154 
Dendritic  fibrous  structures  of  GrubeT; 

47S 
Dental  sac.   244 
Dentin,   239 

development  of,  244 

fibrils  of.  demonstration  of,  303 
Dentinal  fibers,  240 

papilliE,   243 

tubvdes,  240 
Dermis,  379,  382 


5o8 


INDEX. 


Descemet's  membrane,   450 
endothelium  of,  451 
technic  of,  474 
Descending  anterolateral  columns,  411 

limb  of  Henle's  loop,  327 
Deutoplastic  granules,  349 
Dextrin  method    of  fixing   celloidin  sec- 
tions, 40 
paraffin  sections,  40 
Diapedesis,   193 
Diaphragm,   1 7 

iris,   18 
Diaster,  69,  374 
Diffuse  cells  of  retina,   464 

spongiblasts,  464 
Diffusion,  currents  of,  29 
Digestion     method     for     demonstrating 
connective-tissue  framework  of  organs 
and  tissues,  129 

sUde,  for  connective  tissue,  129 
Digestive  organs,  235 
technic  of,  303 

tract,  glands  of,  technic  for,  304 
Dilator  muscle  of  pupil,  455 
Direct  cerebellar  columns,  411 

pyramidal  tract,  411 
Discus  proligerus,  347 
Dispirem,   69 
Distilled  w^ater  for  fixing  paraffin  sections 

to  slide,  39 
Dorsal  utriculus,  496 
Double  knife,  21 

staining,  44 
of  cells,   76 
Doyere's  elevation,   162 
Duct,   alveolar,    314,   315 

BarthoHn's,   253 

bile-,  296 

cochlear,  484,  485 

ejaculatory,  368 

excretory,  367 

Gartner's,  360 

intralobular,  of  pancreas,  300 

nasal,  474 

pancreatic,  298 

Steno's,   253 

utriculosaccular,  481 

Wharton's,  253 

Wirsungian,  298 

Wolffian,  360 
Ductus  endolymphaticus,  476 
Dura  mater,  nerves  of,  437 
spinal,  436 


Ear,  476 

external,  476 
technic  for,  497 

internal,  480 

middle,  478 

technic  for,  497 

technic  for,  497 

vestibule  of,  480 
Ectoderm,   79 

tissues  derived  from,   79 
Egg  tubes,  primary,  of  Pflüger,  345 


Ehrhch-Biondi-Heidenhain    three-color 

mixture,   229 
Ehrlich 's  granulations,  227 
hematoxylin,  43 

for  nuclei  and  granules,  228 
leucocytic  granules,   192 
methylene-blue  stain  for  nervous  tissues, 

182 
neutrophile  mixture,  229 
Ejaculatory  ducts,  368 
Elastic  elements,  technic  for,  235 
fibers,   100 

in    cartilage,    picrocarmin    as    stain 

for,   131 
respiratory,  demonstration  of,  322 
membrane,  anterior,  of  cornea,  449 

posterior,   of  cornea,   450 
tissue,  effect  of  trypsin  digestion  on,  127 
method  of  obtaining,   127 
Enamel,   238 
cells,  243 
germs,   243 
prisms,   238 
technic  of,  303 
Encoche  d'ossification,  121 
End-brush,  162,  167,  237 
End-bulbs  of  Krause,  170,  388 

cylindric,   172 
Endocardium,   213 

lymphatic  netvs^orks  in,   215 
Endochondral  bone,   116 
bone-development,   116 
Endolymph,  495 
Endomysium,   143 
Endoneurium,   160 
Endoplasm,  62,  98,   210 
End-organ  of  Ruffini,  388 
Endosteum,   207 
Endothehal  cells,  80,  94 

and    mesothelial    cells,    method    of 

studying  relations,  95 
demonstration  of,  95 
technic  for,   233 
Endothehum,  92 

anterior,  of  iris,  455 
of  Descemet's  membrane,  451 
of  intima,   technic  for,   235 
End-piece  of  Retzius,  361 
End-plate,   motor,    163 
Engelman,  accessory  disc  of,   139 
Entoderm,  58,   79 

tissues  derived  from,  80 
Eosin   as  stain  for  blood -cells,    227 
Eosinophile    granules,    193 
cells  with,  209 
technic  for,  227 
Epicardium,  214, 
Epidermis,  379 

nerves  of,   technic  of,   405 
of  cutaneous  layer  of  tympanic  mem- 
brane, 476 
technic  of,  403 
Epidural  space,  437 
Epilamellar  plexus,    261,    397 
Epimysium,    143 
Epiphyses,   development  of,    121 


INDEX. 


509 


Epiphysis,  422 

Epithelial   cells   in    small   intestine,    275 
isolated,  examination  of,  95 
processes,    interpapillary,    85 
Epithelium,  anterior,  of  crystalline  lens, 
468 
ciliated,  islands  of,  in  cervical  canal,  356 
classification,  81,  82 
columnar,    pseudostratified,    S3 
simple,  83 
stratified,  85 
corneal    tech  nie    of,    474 
germinal,    examination  of,   378 

of  ovar}',  345 
glandular,  87 
neuro-,  92 

of  alveoU  of  mammary  gland,  401 
of  cornea,   449 

of  kidney,  demonstration  of,  343 
of  mucous  membrane  of  intestine,  274 
leucocytes  in,   275 
of  vagina,  358 
of  olfactor)'   region,    498 
of  urethra,  371 
of  vestibule  of  vagina,   360 
posterior,  of  iris,  455 
respiratory,  315 

examination,  of,  322 
simple,  82 
columnar,  83 
cubic,  82 
squamous,  82 
stratified,  83 
columnar,  85 
squamous,   84 
technic  of,   94 
transitional,  85 
Eponychium,  395 
Epoophoron,  344,  360 
Erlicki's  fluid,   26 
Er}'throblasts,   208 
Erythrocytes,   187 
diameter  of,    190 
effect  of  acetic  acid  on,   188 
of  alkahes  on,   189 
of  bile  on,   188 
of  fluids  on,   188 
of  tannic  acid  on,  189 
of  water  on,  1S8 
examination  of,   226 
fresh,  fixation  of,  226 
method  of  counting,   232,   233 
size  of,   190 
stroma  of,   187 
technic  for,  226 
Esophagus,  262 

method  of  examining,  305 
Eustachian  tube,  479 

mucous  membrane  of,  470 
Excavation,    physiologic,    of    retina,    460 
Excretory  ducts,   367 
Exoplasm,  62,  98,  210 
External  ear,  476 

technic  for,   497 
External    Hmiting    membrane  of   retina, 
459,  462 


External  semicircular  canal,  480 
Extra-epitheUal  glands,  88 
Eye,  446 

anterior  lymph-channels  of,  469 

development  of,  446 

fetal  blood-vessels  of,   468 

general    structure    of,    446 

pigment  membrane  of,  446,  447,  457 

protective  organs  of,  469 

technic  for,  474 

tunica  externa  of,   446 
fibrosa  of,  446,  448 
interna  of,  446,  457 
vasculosa  of,  446,  452 

tunics  of,  446 
Eyeball,   446 

interchange  of  fluids  in,  469 
Eyelids,  469 

blood-supply  of,  473 

conjunctival  portion  of,  470 

cuticular  portion  of,  470 

middle  layer  of,  471 

third,  473 


Fallopian  tubes,  354 
blood-supply  of,  355 
mucous  membrane  of,  354 
muscular  coat  of,   355 
treatment  of,  378 
Farrant's  gum  glycerin,   53 
Fasciculus  gracilis,  411 
Fat,  absorption  of,  by  intestine,  2S8 
method  of  studying,  306 
lobules,   1C7 
of  cells,  61 

Sudan  III  as  stain  for,    130 
Fat-cell,  scheme  of,   107 
Fat-marrow,   207 
Female  genital  organs,  344 

pronucleus,  74 
Fenestra  cochleae,  479 
rotunda,  479 
vestibuli,  478 
Fenestrated  membranes,  107 
,  Ferrein,  pyramids  of,  324 
FertiKzation,  process  of,  71 

diagrams  of,   72,   73 
Fetal  blood-vessels  of  eye,  468 
Fiber-baskets  of  retina,  462 
Fiber-layer,  Henle's,  461 
outer  of,  retina,  461 
Fibers,  arcuate,  of  cornea,  450 

association,   of  cerebral  cortex,   420 
centripetal,     of    cerebral    cortex,    420 
climbing,  of  cerebellar  cortex,  416 
commissural,    of   cerebral   cortex,    420 
cone-,   of  retina,   459 
dentinal,    240 
elastic,    100 

in  cartilage,  picrocarmin  as  stain  for, 

131 
respiratory,  demonstration  of,  322 
heart-muscle,  MacCallum's  nitric  acid 
mixture    for   isolating,    23 


5IO 


INDEX. 


Fibers,  lens,  468 
mantle,   69 

mossy,  of  cerebellar  cortex,  416 
motor,    162 
Müller's,  454,  462 
muscle-,  intrafusal,   175 

nonstriated,  demonstration  of,  148 

striated,  tcchnic  of,  147 

striped,   136 

voluntary,  development  of,  144 
nerve-,   157 

ending  in   muscular   tissue,    162 

meduUated,  demonstration  of,  180 
of  teeth,   242 

methylene-blue    stain    for,    184 

nonmedullated,    160 
demonstration  of,    182 

of  hair  follicles,  393 

of  utriculus,  483 
neuroglia,  Benda's  method  of  staining, 

445 
Mallory's  methods  of  staining,  445 
of  olfactory  nerve,  staining  of,  182 
perforating,  of  cornea,  450 
peripheral,  of  olfactory  bulb,  421 
projection,  of  cerebral  cortex,  419 
Purkinje's  213 

isolated  demonstration  of,  148 
muscle-cells  of,  147 
Remak's,   160 

demonstration  of,   182 
reticular,    of   liver,    demonstration    of, 

308 
rod-,  of  retina,  458 
Sharpey's,  115 

method  of  isolating,  134 
sustentacular,  492 
terminal,    of   cerebral    cortex,    420 
tunnel-,  494 
white,  99 

rami,  429,  456 
Fibrse  circulares,  454 
Fibril  bundles,   140 

Fibrillar    elements    of    nervous    system, 
Apathy's    method    for    demonstration 
of,  442 
Fibrils,  axis-,   157 

of  axial  cord,  demonstration  of,  181 
of  dentin,  demonstration  of,  303 
Fibrin,    demonstration  of,    23 t 
Fibrocartilage,  white,   no 
Fibro-elastic  cartilage,  no 
P'ibrous  connective  tissue,  loi 

tissue  elastic,   106 
Filiform  papillae,   24S 
Films,  blood,  Wright's  method  of  stain- 
ing, 229 
Filum  terminale,  406 
Fimbriae  linguae,   249 
Fissure,  choroidal,  447 
Fixing  methods,  23 
solutions,   23 

acetic  sublimate,   25 
alcohol,   23 

Bütschli's    foam-structure,   for  cells, 
79 


Fixing  solutions,  Carnoy's  acetic-alcohol, 

23 

Carnoy's    acetic    acid-alcohol-chlo- 
roform,  23 

chromic  acid,  26 
for  cells,   75 

corrosive  sublimate,  24 
for  cartilage,   130 
for  cells,   75 

Erlicki's,   26 

Flemming's  24 
for  cells,   75 

Fol's,   24 

formalin,  27 

formol,   27 

Hayem's,  226 

Hermann's,   24 

Müller's,  26 

nitric  acid,   26 

osmic  add,   24 
for  cartilage,   130 

picric  acid,   25 
for  cells,   75 

picric-nitric  acid,   25 

picric-osmic-acetic  acid,   25 

picric-sublimatc-osmic  acid,   25 

picrosulphuric  acid,   25 

potassium  bichromate  and  formalin 

27 
Rabl's,  25 
Tellyesnicky's,   26 
vom  Rath's,  25 
Zenker's,   26 
Flagellate  cells,  60 
Flagellum  of  spermatosome,  361 
Flemming's  germ  centers,    194 
solution,   24 

for  fixing  cells,    75 
Flower-like  nerve-ending,   178 
Fold,  semilunar,  484 
Foliate  papillce,   249 
Follicles,  Graafian,  347 
bursting  of,  352 
hair,  389 

nerve-fibers  of,  393 
lymph-,  germ  centers  of,  technic   for, 

234 
of  mucosa  of  vermiform  appendix, 

281 
of  tongue,  251 
of  tonsils,   251 
solitary,   197 

technic  for,   306 
ovarian,  atresia  of,  353 
simple,   197 
Follicular  cells,  372 

glands,  Qi 
Folliculi  linguales,   251 
Fol's  solution,   24 
Fontana's  spaces,  455 
Foramen  apicis  dentis,   238 
Foramina  nervosa,  488 

papillaria,  330 
Formalin  as  fixing  solution,  27 
Formol  as  fixing  solution,  27 
Fovea  centralis,  460 


INDEX. 


511 


Foveolas  of  stomach,   266 
Fragmentation,  direct,  of  nucleus,  71 
Freezing  apparatus  for  sliding  microtome, 

Friedländer's  glycerin-hematoxylin,  43 

Front  lens,   19 

Fuchsin-resorcin  elastic  fibers  stain,   128 

Fundamental  lamells;,   113 

Fundus  glands  of  stomachj  268 

of  fovea  centralis,  460 
Fungiform  papillte,  248 
Funiculi,  of  nerve-trunk,    160 

compound,  162 
Funnels,  pial,  439 
Future  periosteum,   116 


Ganglia,  424 
spinal,  424 
sympathetic,  427 
Ganglion  cell,   149 

demonstration  of,   182 
la3'er  of  retina,  459,  464 
of  Dogiel,  in  spinal  ganglia,  426 
spiral,  of  cochlea,  494 
Gartner's  duct,  360 
Gastric  mucous  membrane,   266 
Gastrulation,   79 

Gay's  circumanal  glands,   282,  398 
Gelatin-Berlin  blue  as  injection  fluid,  54 
Gelatin-carmin  as  injection  fluid,  54 
Gelatinous  bone-marrow,  210 
substance  of  Rolando,  408 
Genital  corpuscles,   171 
organs,  female,  344 
male,  361 
Genito-urinary  organs,   323 

•    technic  of,  342 
Gerlach's  method  of  impregnation,  48 
Germ  center,   197 

of  Flemming,    194 
of  lymph-follicles,  technic  for,   234 
enamel,  243 
hair,  389 
layers,  58 
primary,    79 
Germinal  epithelium,  examination  of,  378 
of  ovary,   345 
vesicle,    71 
Giant  cells,   209 
Gianuzzi,  crescents  of,   256 
Giraldes,  organ  of,  367 
Gitterfasern,  301 

Glands,  alveolar,  91.     See  also  Alveolar 
glands. 
axillary,   398 
capsule  of,  92 
carotid,   225 
ceruminous,   389,   476 
ciliary,   398,   454 

Moll's,  470 
circumanal,   282,  398 
coil-,  396 

extra-epithelial,  88 
follicular,  91 
hemal,   200 


Glands,  hemolymph,  200 

structure  of,   201 
injection  of,  55 
intra-epithelial,  88 
lacrimal,  473 

accessory,  470 

nerve  supply  of,  473 
lenticular,   271 
lymph-,   196,   197 

blood  supply  of,   200 

capsule  of,   198 

hilum  of,   197 

lymph-sinuses  of,   199 

marrow,   201,  202 

technic  for,   233 

trabeculae  of,   198 

with  blood-sinuses,   200 
mammary,    400.     See    also   Mammary 

gland. 
Meibomian,  472 
mixed,   258 
mucous,   255 
multicellular,  88 

classification,  91 
of  Bartholin,  360 
of  Bowman,  499 
of  Brunner,   265,   277 
of  Cowper,  370 

of  digestive  tract,  technic  for,  304 
of  Gay,   282,  398 
of  Lieberkühn's,  88,   276 
of  Moll,  308,  470 
of  Montgomery,   402 
of  mouth,  small,  259 
of  oral  cavity,   253 
of  skin,  396 
of  stomach,   267 

cardiac,   267 

fundus,   268 
of  Tyson,  372 
parathyroid,  321 
parotid,   255 
peptic,   268 
pineal,  422 

prostate,  368.     See  also  Prostate. 
pyloric,   269 
salivary,   253,   255 

blood  supply  of,   259 

nerve  supply  of,   260 
sebaceous,   39S 
serous,   255 
splenolymph,   201 
structure  and  classification,  88 
sublingual,   255 
submaxillary,   25S 
sudoriparous,    396.     See    also    Siceaf- 

glauds. 
suprarenal,   339.     See  also  Suprarenal 

glands. 
sweat-,  396.     See  slIso  Sii'eat-glands. 
tarsal,  472 
thymus,   210 

blood  supply  of,   212 
thyroid,  319.     See  also  Thyroid  gland. 
tubular,  89.     See  also  Tubular  glands. 
tubulo-alveolar,  90 


512 


INDEX. 


Glands,  unicellular,  87 
Glandula  carotica,  225 
Glandulae  buccales,  236 

duodenales,   265 

labiales,   236 
Glandular  cells,  61 

epithelium,  87 
Glassy  layer  of  choroid,  452,  453 

membrane  of  hair,  391 
GKsson's  capsule,   289 
Glomerular  layer  of  olfactory  bulb,  421 
GlomeruU  arteriosi  cochleee,  495 
Glomerulus,  323 
Glomus  caroticum,   225 
Glycerin,  Farrant's  gum,  mounting  in,  53 

mounting  in,  53 
Glycerin-albumen  for  fixing  paraffin  sec- 
tions to  shde,  38 
Glycogen     in     cartilage,     iodo-iodid     of 
potassium  stain  to  demonstrate,  131 

in  liver-cells,  demonstration  of,  306 

of  cells,   61 
Goblet  cells,  87,   265 
Gold  chlorid  as  stain  for  capsules  of  car- 
tilage,  131 
method  of  impregnation,  48 
Golgi-Mazzoni  corpuscle,  388 
Golgi-nets,   Bethe's  method  of  staining, 

443 
Golgi's  cells,   408,  418,  419 

chromsilver  or  chromsublimate  method 

of  impregnation,  49 
gold  chlorid  method  of  impregnation,  48 
methods  of  impregnation,  49,  50 
mixed  method  of  impregnation,  50 
potassium  bichromate  and  bichlorid  of 
mercury   method   of   impregna- 
tion, 50 
method  of  impregnation,  49 
preparations.  Ruber's  method  of  per- 
manently   mounting    under    cover- 
glass,  51 
rapid  method  of  impregnation,  50 
slow  method  of  impregnation,  50 
Goll's  column,  411 
Gower's  column,  411 
Graafian  follicle,  347 
bursting  of,  352 
Grandry's  corpuscles,  technic  of,  405 
Granular  cells  of  cerebellar  cortex,    416 
layer  of  cerebellar  cortex,  416 
of  olfactory  bulb,  421 
Tomes',   246 
sole  plate,   163 
Granulations  of  leukocytes,  227 
Granules,  acidophile,  technic  for,  227 
amphophile,  technic  for,  228 
basichromatin,  63 
basophile,   193 
cells  vdth,   209 
technic  of,  228 
chromatophile,   149 
deutoplastic,  349 
eosinophile,   193 
cells  with,  209 
technic  for,  227 


Granules,  in  cells,  Altmann's  method  of 
demonstrating,   77,   78 

induhnophile,  technic  for,  228 

interstitial,  Kölliker's,   141 

leukocytic,  Ehrlich's,   192 

neutrophile,   193 
technic  of,  228 

oxychromatin,  63 

Schrön's,  344 

tigroid,   149 

zymogen,   in    pancreas,   demonstration 
of,  308 
Gray  nuclei,  central,  of  cerebellar  cortex, 
416 

substance  of  spinal  cord,  406,  409 
Grenacher's  alum-carmin,  42 

as  stain  for  bulk,  46 
Ground  bundle,  anterior,  411 

plexus  of  cornea,  451 
Ground-substance  interfascicular,   105 

of  areolar  connective  tissue,   102 

of  cartilage,  changes,  in,   in 
Gruber's  dendritic  fibrous  structure,  478' 
Gscheidtlen's  method  of  obtaining  hemo- 
globin crystals,   230 
Gum  glycerin,  Farrant's  mounting  in,  53 


Hair,  389 

auditory,  490 

bulb,  389,  393 

club,  393 

cortical  layer  of,  389 

cuticle  of,  389 
inner,  390 

folhcle,  389 

nerve-fibers  of,  393 

germ,  389 

glassy  membrane  of,  391 

growth  of,  392 

medullary  substance  of,  390 

olfactory,  499 

papilla,  389 

root,  389 

root-sheaths  of,  389 
inner,  390 
outer,  390 

shaft,  389 

shedding  of,  393 

technic  for,  404 
Hair-cells  of  utriculus,  483 
Hamulus,  484 
Hassal's  corpuscles,   212 
Haversian  canals,   112 

spaces,   120 
Hayem's  solution,   226 

for  diluting  blood,   232 
Hearing,  organ  of,  476.     See  also  Ear. 
Heart,   186,  213 

auriculoventricular  valves  of,   213 

blood  supply  of,  214 

elastic  tissue  of,   214 

muscle,   145 

motor  nerve-supply  of,   166 

muscle-cells,  demonstration  of,   148 

muscle-tissue,  development  of,   146 


INDEX. 


513 


Heart,   nerve  supply  of,  215 
Heart-muscle  fibers,  MacCallum's  nitric 

acid  mixture  for  isolating,  23 
Heidenhain's  demilunes,   256 
iron  hematoxylin,  43 

as  stain  for  bulk,  46 
median  membrane,   137 
Helicotrema,  485 
Heliotropism,   61 
Heller's  plexus,   283 
Hemal  glands,     200 
Hemalum,  acid,  as  stain,  43 
as  stain,  43 
in  bulk,  46 
Hematin,   187 
Hematoblasts,   194 
Hematoidin  crystals,   231 
Hematoxylin  as  stain,     42.     See     also 

Stai?is. 
Hematoxylin-eosin  as  stain,  45 
Hematoxylin-safranin  as  stain,  46 
Hemin,   18S 

crystals,  method  of  obtaining,  230 
Hemocytometer,  Thoma-Zeiss,   232 
Hemoglobin,   187 

crystals,  method  of  obtaining,   230 
demonstration  of,  230 
nucleated    red    blood-cells    containing, 
208 
Hemokonia,   195 
Hemolymph  glands,   200 

structure  of,   201 
Henle's  fiber  layer,  461 
layer,  390 
loop,  323 

descending  limb  of,  327 
sheath,   162 
Hensen's  cells,  491,  492 

median  disc,   137 
Hepatic  artery,  293 
cells,  cords  of,   290 
cords,  290 
Herbst's  corpuscles,   174,  389 

technic  of,  405 
Hermann's  solution,   24 
Heterotypic  mitosis,  70 
Hilum  of  lymph-glands,   197 
Histology,  general,  58 

special,   186 
Homeotypic  mitosis,   70 
Honing  microtome  knife,  37 
Horizontal  cells  of  retina,  464 

semicircular  canal,  480 
Horns  of  spinal  cord,  40S 
Howship's  lacunae,   120 
Hoyer's  yellow  gelatin  mass,  54 
Huber's  method  of  permanently  mount- 
ing Golgi's  preparations  under  cover- 
glass,  51 
Humor,   aqueous,   446 
Huschke's  auditory  teeth,  488 
Huxley's  layer,  390 
Hyaline  cartilage,   108 
Hyaloid  arteries,  anterior,  468 
posterior,   468 
canal,  468 

33 


Hyaloid  membrane  of  vitreous  body,  467 
Hydatids  of  Morgagni,  360 
Hydrochloric  acid,    action    of,    on    con- 
nective tissue,   128 
as  decalcifying  fluid,   132 
as  macerating  solution,   23 
Hydrotropism,  61 
Hymen,  359 

Hypolamellar  plexus,   261 
Hypophysis,  423 
chief  cells  of,  423 
chromophihc  cells  of,  423 
circulation  of,  424 


Imbedding,  27 
celloidin,  30 

diagram  for,  32 
celloidin-parafi&n,  32 
paraffin,   27 

diagram  for,  30 
Immersion  lens,   19 

Impregnation,  Cohnheim's  method,  48 
Cox's  method  51 
Gerlach's  method,  48 
gold  chlorid  method,  48 
Golgi's     chromsilver    or    chromsubli- 
mate  method,  49 
gold  chlorid  method,  48 
methods,  49 
mixed  method,  50 
potassium  bichromate  and  bichlorid 

of  mercury  method,  50 
potassium  bichromate  method,  49 
rapid  method,  50 
slow  method,  50 
Kopsch's  method,  52 
Kühne' s  method,  48 
Löwit's  method,  48 
methods  of,  47  '       . 

of  bile  capillaries,  307 
Ran  vier' s  method,  48 
silver  nitrate  method,  47 
Indifferent  fluids,   21,   22 
Kronecker's,   22 
physiologic  sahne  solutions,   22 
Ranvier's  solution  of  iodin  and  po- 
tassium iodid,   22 
Ripart  and  Petit's,  22 
Schnitze' s  iodized  serum,   22 
Induhnophile  granules,  technic  for,    228 
Inferior  nasal  artery  of  retina,  466 
vein  of  retina,  466 
papillary  artery  of  retina,  466 

vein  of  retina,   466 
vertical  semicircular  canal,  480 
Infiltration,   27 
celloidin,  30 

diagram  for,  32 
celloidin-paraffin,  32 
paraffin,   27 

diagram  for,   30 
Injection  fluids,  53 
Altman's,  55 
Berlin  blue,  53 
carmin  mass,  cold,  54 


514 


INDEX. 


Injection  fluids,  gelatin-Berlin    blue,  54 
gelatin-carmin,  54 
silver  nitrate,   55 
yellow  gelatin  mass,  54 
Injection  method  for  demonstration     of 
bile  capillaries,  306 
of  distribution   of  hepatic   blood- 
vessels, 306 
methods  of,  53 
of  animals,  54 
of  glands,  55 
of  lymph-channels,  .55 
of  lymph-spaces,  55 
of  lymph-vessels,  55 
of  organs,  55 
Inner  molecular  layer  of  retina,  464 
nuclear  layer  of  retina,  459,  462 
scleral  sulcus,  449 
Intercellular  bridges,  81,  380 
demonstration  of,  96 
spaces,  81 
substance,   79 
Interfascicular  ground-substance,  105 
Interglobular  spaces  of  Czermak,  241 
Interlobular  arteries  of  kidney,  332 
veins  of  kidney,  334 
of  liver,   293 
Intermediate  tubule  of  pancreas,  300 
Internal  auditory  artery,  494 
ear,  480 

limiting  membrane  of  retina,  462 
Interpapillary  epitheUal  processes,  85 
Interstitial  granules  of  KöUiker,   141 
Intertubular  cell-masses  of  pancreas,  301 
Intestine,   264 

absorption  of  fat  by,   288 
blood  supply  of,   283 
large,   281 

blood-vessels  of  mucosa  of,   284 
lymph-.vessels  of,  284 
lymph  supply  of,   283 
mucous    membrane    of,  general   struc- 
ture,  264 
nerves  of,  demonstration  of,  306 
muscularis  mucosEe  of,   265 
nerve  supply  of,   283 
secretion  of,   288 
small,   274 

axial  canals  of,   285 
basement  membrane  of,   278 
epthelial  cells  in,   275 
lymphatics  of,   285 
lymph-nodules  of,   279 
mucous  membrane  of,   274,   277 
blood-vessels  of,   284 
epithelium  of,   274 

leucocytes  in,   275 
lymph -nodules  of,   279 
villi  of,   274 
muscularis  mucosre  of,   279 
villi  of,  lacteals  of,  285 
with  villi,   fixation  of,   305 
stratum  circulare  of,  266 
fibrosum  of,   265 
longitudinale  of,  266 
submucosa  of,   265 


Intestine,  tunica  mucosa  of,  265 
Intirha,  endothelium  of,  technic  for,  235 
Intracapsular  plexuses,  429 
Intracartilaginous  bone,   116 
Intra-epithelial  glands,  88 
Intrafusal  muscle-fibers,   175 
Intralobular  duct  of  pancreas,  300 
Intramembranous  bones,   116,   122 

bone-development,   122 
lodo-iodid  of  potassium  stain  to  demon- 
strate glycogen  in  cartilage,   131 
Iris,  446,  452-455 

anterior  ^dothelium  of,  455 

diaphragm,   18 

nerve  supply  of,  456 

posterior  epithelium  of,  455 

stroma  of,  455 
Islands  of  ciliated  epithelium  in  cervical 

canal,  356 
Isotropic  intermediary  disc,   138 


Jacobson' s  organ,  499 
Japanese  method  of  fixing  paraffin  sec- 
tions to  slide,  39 
Jelly,  Wharton's,   100  , 


Kaes  and  B echter eff's  striation,  421 

Karyokinesis,  64 

Karyokinetic     cell-division,     heterotypic, 

374 
homeotypic,  374 
Karyolysis,   74 
Karyosomes,  63 
Keratohyalin,  380 
technic  for,  403 
Kidney,   323 

arched  collecting  portion  of  tubules,  323 

329 
blood-vessels  of,  332 
cortical  substance  of,  323,  324 
distal  convoluted  portion  of  tubules, 

323.  329 
epithelium  of,  demonstration  of,  343 

intercalated  portion  of  tubules,  323,  329 

interlobular  arteries  of,  332 

veins  of,  334 
lymphatics  of,  334 
medullary  substance  of,  323 
nerves  of,  334,  335 
pelvis  of,  336  - 

mucosa  of,  337 

blood-vessels  of,  338 
proximal  convoluted  portion  of  tubules, 

323.  325 

secretory  processes  of,  335 

straight  collecting  tubules  of,  323 

technic  of,   342 

tubules  of,  demonstration  of,  342 

vasa  afferentia  of,  332 
Knife,  double,   21 

microtome,  honing  of,  37 
sharpening  of,  37 
KölKker's  interstitial  granules,   141 

muscle-columns,   140 


INDEX. 


515 


Kölliker's  neuropodia,   151 
KoUmann's  cold  carmin  mass,  54 
Kolossow's  method  of  demonstrating  in- 
tercellular bridges,  96 
Kopsch's  method  of  impregnation,  52 
Krause,  end-bulbs  of,   170,  388 
cylindric,   172 
membrane  of,   137 
Kronecker's  fluid,   22 
Kühne' s  method  of  impregnation,  48 
Kupffer's  stellate  cells,   295 
Kytoblastema,  64 


Labium  tympanicum,  487 

vestibuläre,  487 
Laboratory  microtome,  33 
Labyrinth,  bony,   480 
development  of,  496 
membranous,  480,  481 
blood-vessels  of,  494 
technic  for,  497 
osseous,  480 
technic  for,  497 
Lacrimal  apparatus,  473 
glands,  473 
accessory,  470 
nerve  supply  of,  473 
sac,  474 
Lacteals  of  villi  of  small  intestine,  285 
Lacunae,  Howship's,   120 

of  bone,   112,   113 
Lamellae,   105 
bone,   113 

compostion  of,   114 
method  of  examining,  131 
circumferential,  inner,   113 

outer,   113 
concentric,   113 
fundamental,   113 
periosteal,   113 
Lamina  basilaris  propria,  489 
choriocapillaris,  452,  453 
cribrosa,  448,  465 
elastica  interna,   218 
fusca,  448 
propria  of  oral  cavity,   236 

of  tympanic  membrane,  477 
reticularis,  48g,  493 
spiralis  meinbranacea,  485 

ossea,  484,  486 
suprachoroidea,  448,  452 
vasculosa  Halleri  of  choroid,  452 
Langerhans,  areas  of,  301 

cells  of,  300 
Large  intestine,  281.     See  also  Intestine, 

large. 
Larynx,  309 

cartilages  of,  310 
demonstration  of,  322 
mucous  membrane  of,  309 
nerves  of,  311 
vascular  supply  of,  310 
Lateral  column,  408 

mixed,   411 
Ledges,  terminal,  86 


Lens,  446 

apochromatic,   19 
capsule,  468 
collective,   19 
crystalline,  467 

anterior  epithelium  of,  468 
fibers,  468 
front,   19 
immersion,   19 
ocular,   19 

suspensory  ligament  of,  467 
technic  of   475 
Lenticular  glands,   271 
Leucocyte-nucleus,  polymorphism  of,  193 
Leucocytes,   191 

granulations  of,  227 

in  epithelium  of  mucous  membrane  of 

small  intestine,   275 
method  of  counting,   232,  233 
mononuclear,   192 
motility  of,    193 
size  of,   192 
transitional,   192 
with  polymorphous  nuclei,   192 
Leucocytic  granules,  Ehrlich's,  192 
Leydig's  cells,  470 
Lieberkühn's  glands,  88,   276 
Ligament,  suspensory,  of  lens,  467 
Ligaments,    105 

Ligamentum  nuchae  of  ox,  structure  of, 
106 
pectinatum  iridis,   454 
Spirale,  485,   488 
Limbus  spirahs,   486,   487 
Lime-salts  in  bone,  hematoxylin  as  stain 
for,   132 
isolation  of,   132 
Limiting  membrane,  external,  of  retina, 
459'  462 
internal,  of  retina,   462 
Lines  of  Retzius,   239 

of  Schräger,   239 
Lingual  mucous  membrane,   247 
papillae  of,   247 
papillae,   247 
Linin,   63 

Liquor  folliculi,    347 
Liver,   289 

blood-vessels  of,  distribution    of,  dem- 
onstration,  306 
examination  of,  343 
connective  tissue  of,  294 
interlobular  veins  of,  293 
lobules,   289 
lymphatics  of,   297 
nerves  of,   298 

demonstration  of,   308 
reticular  fibers  of,  demonstration  of,  308 
reticulum  of,    294 
stellate  cells  of,   295 
technic  of,  306 
tissue,  technic  of,  307 
trabeculoe  of,   290 
Liver-cells,  examination  of,  306 

glycogen  in,  demonstration  of,  306 
Loop,  Henle's,  323 


5i6 


INDEX. 


Loop,  Henle's  descending  limb  of,  327 
Lö wit's  method  of  impregnation,  48 
Lugol's  solution  to  demonstrate  glycogen 

in  cartilage,   131 
Lung  alveoli,  314 

blood-vessels  of,  316 

lobules  of,  316 

lymphatics  of,  317 

nerves  of,  317 

structure,  units  of,  316 

tissue  of,  demonstration  of,  322 
Lunula,  395 
Lutein,  3^53 

cells,  353 
Lymph,   186 

canalicular  system,   102 

capillaries,  224 
Lymphatic  netvi'orks  in  endocardium,  215 

system,   223 
Lymph-channels,  anterior,  of  eye,  469 

injection  of,  55 
Lymph-follicles,  germ  centers  of,  technic 
for,  234 

of  mucosa  of  vermiform  appendix,  281 

of  tongue,  251 

of  tonsils,  251 
solitary,   197 

technic  for,  306 
Lymph-glands,   196,   197 

blood  supply  of,  200 

capsule  of,   198 

hilum  of,   197 

lymph-sinuses  of,   199 
marrow,  201,   202 

technic  for,   233 

trabeculae  of,  198 

with  blood-sinuses,   200 
Lymph-nodules,   196 

agminated,   197 

of  mucosa  of  small  intestine,  279 
Lymphocytes,   191,   194 

size  of,   192 
Lymphoid  tissue,   196 
Lymph-sinus,   199 
Lymph-spaces,  224 

injection  of,  55 

periaxial,   176 

perichoroidal,  452 
Lymph-supply  of  intestine,   283 
Lymph-vessels,   186,   223 

injection  of,   55 

of  central  nervous  system,  440 

of  kidney,  334 

of  large  intestine,   284 

of  liver,   297 

of  lung,  317 

of  mammary  glands,  402 

of  mouth,  260 

of  ovary,   354 

of  skin,  386 

of  small  intestine,  285 

of  testes,  367 

of  uterus,  357 


MacCallum's  nitric  acid  mixture,   23 


Macerating  solutions,  22 
alcohol,   22 
caustic  acid,  22 

potash,   22 
chromic  acid,   22 
hydrochloric  acid,  23 
MacCallum's,   23 
nitric  acid,   23 

and  chlorate  of  potassium,   23 
sulphuric  acid,  23 
Maceration,  methods  of,  22 
Macula  acustica  sacculi,  481 
utricuK,  481 
lutea,  460 

region  of,  460 
Magenta  red  as  stain  for  connective  tissue, 

128 
Male  genital  organs,  361 

pronucleus,  73 
Mallory's    differential    stain  for    connec- 
tive-tissue   fibrillae    and    reticulum, 
128 
selective  neurogUa  fiber-staining  meth- 
ods, 445 
Malpighian  corpuscles,  202,  203,  323,  324 

pyramid,  323 
Mammary  gland,  400 

alveoli  of,  epithelium  of   401 
lymphatics  of,  402 
nerves  of,  402 
Mantle  fibers,   69 
Marginal  thread  of  spermatosome,  361 

zone,  81 
Marrow,    bone-,    207.      See    also    Bone- 
marrow. 
fat-,   207 

lymph-glands,   102,   202 
spaces,  primary,   118 
secondary,   120 
Marrow-cells,   208 
Martinotti's  cells,  418,  419 
Mast-cells,   104 

granules,   technic  of,   228 
Matrix  of  areolar  connective  tissue,   102 
of  nail,  394 
sulcus  of,  394 
Mature  ovum,  351 

Mayer's  solutions  for  staining  mucin,  305 
Median  disc  of  Hensen,  137 

membrane  of  Heidenhain,  137 
Mediastinum  testis,  363 
Medullary  cords,   199 
rays,  323 
sheath,   157 
technic,  440 
Benda's,  442 
Pal's,  442 
Weigert's,  440,  441 
substance  of  cerebellar  cortex,  416 
of  cerebral  cortex,  419 
of  hair,  390 
of  kidney,  323 
of  ovary,  344 
Meibomian  gland,  472 
Meissner's  corpuscles,    170,   387 
technic  of,  405 


INDEX. 


5^7 


Meissner' s  plexus,   287 
Membrana  capsulopupillaris,  468 
praeformativa,   244 
prima,  81 
propria,  88,  92 
of  pancreas,  301 
of  uriniferous  tubules,  330 
pupillaris,  468 
tectoria  Cortii,  489,  493 
Membrane,  basement,  81,  88 
of  small  intestine,  278 
basilar,  488 
Bowman's,  449 
cell,  absence  of,  62 
Corti's,  489,  493 
Descemet's,  450 

endothelium  of,  451 
technic  of,  474 
elastic,  anterior,  of  cornea,  449 

posterior,  of  cornea,  450 
external  limiting,  of  retina,  459,  462 
fenestrated,   107 
glassy,  of  choroid,  452,  453 

of  hair,  391 
Heidenhain's,   137 
hyaloid,  of  vitreous  body,  467 
internal  limiting,  of  retina,  462 
Krause's,   137 

median,  of  Heidenhain,   137 
mucous.     See  also  Mucous  membrane. 
Nasmyth's,   238 
nuclear,  63 

of  central  nervous  system,  436 
oral  mucous,   fixation  of,   303 
otolithic,  483 
peridental,   242 

pigment,  of  eye,  446,  447,  457 
Reissner's,  485,  489 
rudder,  of  spermatosome,  361 
tympanic,  476.       See    also    Tympanic 

membrane . 
undulating,  of  spermatosome,  361 
vestibular  (Reissner's),  485,  489 
vitreous,   452,   453 
Meninges  of  central  nervous  system,  436 
Menisci,  tactile,  387 
technic  of,  405 
Merkel's  terminal  disc,   139 
Mesameboid  cells,  80 
Mesenchymatous  tissue,  97 
Mesenchyme,   80 
Mesoderm,  58,   79 

cells  of,  80 
Mesothelial  cells,  80 

and    endothelial    cells,     method    of 
studying   relations,    95 
Mesothelium,   80,   92 
Metakinesis,   68 
Metaphases,   65,  68 

Methylene-blue     stain,      Ehrlich's,      for 
nervous  tissues,   182 
for  nerve-fibers,    184 
Methyl-green  as  stain,   44 
Metschnikoff's   phagocytes,    60 
Meyer's     method     of     staining     nerve- 
fibers,   184 


Microcentrum,   191 

Microscope  and  its  accessories,  17 

coarse  adjustment  of,    18 

compound,    17 

description  of,    17 

fine  adjustment  of,  18 

parts  of,    17 

simple,   17 
Microscopic  preparation,  21 

preparations  of  undccalcified  bone,  131 

technic,   introduction  to,    17 
Microtome,   32 

knife,  honin?  of.  37 
sharpening  of,   37 

laboratory,  33 

Minot  automatic  precision,   33,  34 
rotary,  34,  35 

precision,  33 

rocking,   33 

rotary,  35 

sliding,    T,T, 

cutting    celloidin    sections    with,    36 

paraffin   sections   with,    35 
freezing   apparatus   for,    36 
Middle  ear,  478 

technic  for,  497 
Migratory  cells,   103,   104,   193 
Milk,  402 

secretion,  401 
Minot    automatic    precision    microtome 

33'   34 
rotary  microtome,  34,  35 
Mitochondria,   60 
Mitosis,   64 

demonstration  of,   75 
heterotypic,   70 
homeotypic,    70 
Mitotic   cell-division  of  fertilized  white- 
fish  eggs,   66,    67 
ten  stages  of,  65 
Mitral  cells,  421 

of  olfactory  bulb,  42j^ 
Mixed  gland,   258 

lateral  column,  411 
Modified   sweat-glands,    398 
Modiolus,   484 

Molecular  layer,  inner,  of  retina,  464 
of  cerebellar  cortex,  413 
of  cerebral  cortex,  417 
of  olfactory  bulb,   421 
outer,  of  retina,  45,  462 
movement  of  cells,  61 
Moll's  glands,  398,  470 
Monaster,  68 

Mononuclear  leucocytes,  192 
Monostratified  cells  of  retina,  464 
Montgomery's  glands,  402 
Morgagni,  hydatids  of,  360 
Morula  mass,   79 

Mossy  fibers  of  cerebellar  cortex,  416 
Mother  cell,  374 
nucleus,  64 
skein,  67 
Motor  end-plate,  163 
fibers,    162 
nerve-endings,    162 


5i8 


INDEX. 


Motor  nerve-endings,  staining  of,   182 
neurones.   153 
peripheral-,   1 62 
diagram  of,   163 
Mounting,   21,  52 
Mouth,  glands  of,  small,  259 

lymphatics  of,   260 
Muchematein,  305 
Mucicarmin,  305 
Mucin,    demonstration   of,    304,    305 

staining  of,   305 
Mucous  connective  tissue,   loc 
gland,   255 

layer  of  tympanic  membrane,  478 
membrane,    gastric,    266 

intestinal,   general  structure  of,   264 
nerves  of,    demonstration  of,   306 
nasal,   technic  of,   500 
of  Eustachian  tube,  479 
of  Fallopian  tubes,  354 
of  larynx,   309 
of  oral  cavity,  236 
of  pelvis  of  kidney,  337 

blood-vessels  of,  338 
of  small  intestine,  274,  277 
blood-vessels  of,  284 
epithelium  of,   274 

leucocytes  in,   275 
lymph-nodules  of,  279 
villi  of,   274 
of  stomach,  fixation  of,  305 
of  tongue,   247 
of  uterus,  355 
of  vagina,  358 

epithehum  of,  358 
of     vermiform     appendix,     lymph- 
follicles  in,   281 
oral,  fixation  of,  303 
Mucus-secreting  cell,  87 
Müller's  fibers,  454 
of  retina,  462 
fluid,   26 
Multicellular  glands,  88 

classification,  91 
Muscle  and  tendon,  relation  of,  method  of 
studying,    148 
ciUary,  454 
dilator,  of  pupil,  455 
heart,   145 

fibers   of,   MacCallum's    nitric   acid 

mixture  for  isolating,   23 
motor  nerve-supply  of,    166 
nonstriated,     motor    nerve-supply    of, 

166 
red,   141 

sphincter,  of  pupil,  455 
striated,     nerve-endings     in,      Sihler's 

method  of  demonstrating,    184 
white,   141 
Muscle-cells,   cardiac,   demonstration  of, 
148 
nonstriated,   134 
of  fibers  of  Purkinje,  147 
Muscle-columns  of  Kölliker,  140 
Muscle-fibers,  intrafusal,  175 

nonstriated,  demonstration  of,   148 


Muscle=fibers,  striated,  technic  of,  147 
striped,   136 

voluntary,  development  of,  144 
Muscular  coat  of  Fallopian  tubes,  355 
of  uterus,  356 
_  of  vagina,   359 
tissue,   134 

destruction  of,  144 
development  of,   144 
heart,   development  of,    146 
nerve-fibers  ending  in,  162 
striated,  blood-vessels  in,   143 
technic  of,   147 
Muscularis  mucosae  of  intestine    265 
of  small  intestine,  279 
of  stomach,    271 
Musculus  ciliaris  Riolani,  471 
orbicularis  oculi,  471 
palpebralis  superior,  472 
Myelin  sheath,   157 
Myelocytes,   208 
Myeloplaxes,   209 
Myoblasts,   144 
Myocardium,   213 


Nail,  394 
bed,  394 

sulcus  of,  394 
body  of,  394 
lunula  of,  395 
matrix,  394 

sulcus  of,  394 
root,  394 
walls,   394 
Nasal  artery,  inferior,  of  retina,  466 

superior,  of  retina,  466 
cavity,  498 

blood-vessels  of,  499 

nerves  of,  500 

technic  of,  500 

vestibule  of,  498 
duct,  474 

mucous  membrane,  technic  of,  500 
vein,  inferior,  of  retina,  466 

superior,  of  retina,  466 
Nasmyth's  membrane,  238 
Nerve  end-organs,  neuromuscular,   174 

neurotendinous,   1 78 
Nerve-cells,      149.     See     also     Ganglion 

cell. 
Nerve-endings,   annulospiral,    178 
flower-hke,   1 78 
in  striated  muscle,  Sihler's  method  of 

demonstrating,   184 
motor,   162 

staining  of,   182 
peripheral,   162 
Ruffini's,  387 
sensory,   1 66 

encapsulated,   169 

free,   168,   169 

staining  of,   182 
Nerve-fibers,   157 

ending  in  muscle  tissue,  162 
layer  of  retina,  464 


INDEX, 


519 


Nerve-fibers,    medullated,   demonstration 
of,   180 

of  teeth,   242 
methylene-blue  stain  for,    184 
nonmeduUated,    160 

demonstration  of,    182 
of  hair  foUicles,  393 
of  utriculus,   483 
Nerves,  auditory,  494 

in    taste-buds,    demonstration   of,    304 
of  bladder,  339 
of  bronchi,   317 
of  ciliary  body,  456 
of  cornea,  451 

technic,  474 
of  dura  mater,  437 
of  epidermis,  technic  of,  405 
of  heart,  215 
of  intestine,  283 

of  intestinal  mucous  membrane,  dem- 
onstration of,  306 
of  iris,  456 
of  kidney,  334,  335 
of  lacrimal  gland,  473 
of  larynx,  311 
of  liver,   298 

demonstration  of,  308 
of  lung,   317 

of  mammary  glands,  402 
of  nasal  cavity,  500 
of  ovary,  354 
of  pancreas,  302 
of  penis,   372 
of  pia  mater,  439 
of  prostate,  370 
of  salivary  glands    260 
of  sclera,  451 
of  skin,  387 

of  suprarenal  glands,   342 
of  tongue,  252 
of  sweat-glands,  397 
of  testes,  367 
of  thyroid  gland,  320 
of  trachea,  311 
of  ureter,  339 
of  uterus,  358 
of  vagina,  360 

olfactory,  staining  fibers  of,  182 
optic,  446,  464 
pilomotor,   394 
supplying  blood-vessels,    223 
Nerve-trunk,   funiculi  of,    160 

compound,    162 
Nervous  system,  central,  406 
blood-vessels  of,  439 
fibrillar     elements     of,     Apathy's 
method   of   demonstrating,    442 
lymph  vessels  of,  440 
membranes  of,  436 
technic  of,   440 
tissue,   148 

Ehrlich's   methylene-blue   stain   for, 
182 

fixation  of,   183 

technic  of,   180 
tunic  of  eye,  446,  457 


Net-knots,  63 

Networks,   technic  for,   235 

Neura,   149 

Neuraxes,   148,   151 

Neurilemma,    158 

Neurilemma-nuclei,    158 

Neuroblasts,    148 

Neurodendron,    149 

Neuro-epithelial  cells,  92 

Neuro-epithelium,   92 

Neurofibrils,  Bethe's  method  of  staining, 

443 
Neuroglia,  434 

fibers,    Benda's    method    of    staining 

445 
Mallory's  methods  of  staining,   445 
staining  of,   444 
Neurogliar  cells,  434 
Neurokeratin,   157 

Neuromuscular    nerve    end-organs,     174 
Neurones,    149 

cell-bodies  of,    149 
independence  of,  theory  of,  156 
motor,    153 

peripheral,  162 
diagram  of,   163 
relationship  of,  431 
sensory,    peripheral,    diagram  of,    167 
Neuroplasm,   157 
Neuropodia,   151 

Neurotendinous  nerve     end-organ,    178 
Neutrophile  granules,  193 
technic  for,   228 
mixture  Ehrlich's,   229 
Nitric  acid  and  chlorate  of  potassium  as 
macerating  solution,   23 
aqueous     solution,     as     decalcifying 

fluid,   133 
as  fixing  solution,   26 
as  macerating  solution,  23 
MacCallum's,   23 
Nodes  of  Ranvier,   158 

demonstration  of,   180 
Nodules,   197 
cortical,    198 
lymph-,   196 
agminated,   197 

of  mucosa  of  small  intestine,  279 
secondary,   197 

terminal,   of  spermatosome,   361 
Normoblasts,   208 
Nuclear  division,   64 

layer,  inner,  of  retina,  459,  462 
membrane,   63 
stains,  41 
Nuclein,  63 
Nucleolus,  58 

true,   63 
Nucleus,   58,   62 

achromatic  portion  of,  63 

chromatoid  accessory,   of  Benda,   377 

contents  of,  62 

daughter,  64 

direct   fragmentation   of,    71 

dorsalis,  408 

gray,  central,  of  cerebellar  cortex,  416 


520 


INDEX. 


Nucleus,    leucocyte-,    polymorphism   of, 

193 
mother,  64 

of  spermatid,  377  , 

resting,  63 
segmentation,   71 
sole,   1 63 
telolemma,   163 
Nuel's  space,  492 


Ocular  lens,  19 
Odontoblasts,   240,   241,  244 
Odontoclasts,   247 
Olfactory  bulb,  421 

glomerular  layer  of,  421 
granular  layer  of,  421 
mitral  cells  of,  421 
molecular  layer  of,  421 
peripheral  fibers  of,  421 
cells,  498 
hairs,  499 
region,  498 

epithelium  of,  498 
nerve,  fibers  of,  staining  of,  182 
Oocytes,  350 
Optic  cup,  447 
nerve,  446,  464 

blood-vessels  of,  465 
papilla,  460 

region  of,  460 
stalks,  446 

vesicles,  primary,  446 
secondary,  447 
Ora  serrata,  461 
Oral  cavity,  235 
glands  of,  253 
mucous  membrane  of,  236 

fixation  of,  303 
submucosa  of,   236 
Orbiculus  ciliaris,  453 
Orcein  as  stain  for  connective  tissue,  128 
Osmic  acid  as  fixative  for  cartilage,  130 
as  fixing  solution,   24 
as  stain  for  adipose  tissue,   130 
Osseous  labyrinth,  480 
Ossicles,  auditory,  478 
Ossification,  centers  of,   116 
groove,   121 
of  cartilage,   11 1 
ridge,   121 
Osteoblasts,   118 
Osteoclasts,   120 
Otolithic  membrane,  483 
Otoliths,  483 
Outer  fiber  layer  of  retina,  461 

molecular  layer  of  retina,  459,  462 
Ovarian  tissue,  fixation  of,  378 
Ovary,   344 

antrum  of,  347 
blood-vessels  of,  354 
cortex  of,  344 
germinal  epithelium  of,  345 
lymphatics  of,   354 
medullary  substance  of,  344 
nerves  of,   354 


Ovary,  stratum  granulosum  of,  345 

stroma  of,  344 

technic  of,  378 
Ovula  Nabothi,  356 
Ovum,   71,  344 

changes   in,  during  development,    350 

mature,  351 

primitive,  345,  350 

ripe,  350 

technic  for,  378 

vacuole  of,  344 
Oxychromatin  granules,  63 


Pacchionian  bodies,  438 
Pacinian  corpuscles,  388 

technic  of,  405 
Pal's     method     for     demonstration     of 

medullary  sheath,  442 
Pancreas,   298 

blood-vessels  of,  302 

cells  of,  inner  and  outer  zones,  methods 

of  differentiating,  308 
intermediate  tubule  of,  300 
intertubular  cell-masses  of,  301 
intralobular  duct  of,  300 
membrana  propria  of,  301 
nerves  of,  302 
technic  of,  308 

zymogen  granules  in,  demonstration  of, 
308 
Pancreatic  duct,   298 
Panniculus  adiposus,  384 
Papilla,  84 

circumvallate,  249 
dentinal,  243 
filiform,   248 
foliate,   24g 
fungiform,  248 
hair,  389 
lingual,  247 
optic,  460 

region  of,  460 
spiralis  cochlea,  481 
tactile,  383 
vascular,  383 
Papillary  artery,  inferior,  of  retina,  466 
superior,  of  retina,  466 
vein,  inferior,  of  retina,  466 
superior,  of  retina,  466 
Paracarmin  as  stain,  42 

in  bulk,  46 
Paradidymis,  367 
Paraffin  imbedding,   27 
diagram  for,  30 
infiltration,    27 

diagram  for,  30 
removal  of,  40 

sections,      cutting     of,      with     sliding 
microtome,  35 
dextrin  method  of  fixing,  40 
distilled  water  for  fixing  of,  to  slide, 

39 
fixing  of  large  numbers  to  cover-slips, 

39 


INDEX. 


521 


Paraffin    sections,    glycerin-albumen    for 
fixing    of,    to   slide,  38 
Japanese  method  of  fixing  to  slide,  39 
Paralinin,  63 
Paranuclein,   63 
Paraplasm,  60 
Parareticular  cells,  464 
Parathyroid  glands,  321 
Paroophoron,  360 
Parotid  gland,  255 
Pars  ciliaris  retinae,  453,  461 

iridica  retinae,  461 

papillaris,   382 

reticularis,  382 
Partsch's  cochineal  solution,  42 
Pellicula,  62 
Pelvis  of  kidney,   336 
mucosa  of,  337 

blood-vessels  of,  338 

renal,  336 
Penis,  370 

erectile  tissue  of,  371 

nerves  of,  372 
Pepsin,    effect   of,    on   connective   tissue, 

128 
Peptic  glands,   268 
Perforating  fibers  of  cornea,  450 
Periaxial  lymph-space,   176 
Pericardium,   214 
Pericellular  plexuses,  428 
Perichondrium,    109 
Perichoroidal  lymph-spaces,  452 
Peridental  membrane,   242 
Perilymph  of  cochlea,  496 
Perilymphatic  spaces,   224 
Perimysium,   143 
Perineurium,   161 
Periosteal  lamellae,   113 
Periosteum,   112 

alveolar,   242 

future,   116 
Peripheral  fibers  of  olfactory  bulb,   421 

motor  neurones,   162 
diagram  of,    163 

nerve  terminations,    162 

sensory  neurone,  diagram  of,  167 
Peritendineum,    105 
Perivascular  spaces,   224 
Petit's  canal,  467 
Petit  and  Ripart's  solution,   22 
Peyer's  patches,   265 
technic  for,  306 
Pflüger's  egg  tubes,  345 
Phagocytes,   193,   194 

Metschnikoff's,   60 
Phalangeal  plate,   491,   492 

process,   49 1 
Pharyngeal  tonsils,   252 
Pharynx,    262 

Physiologic  excavation  of  retina,  460 
Pia  intima,   438 

mater,  438 

nerves  of,  439 
Pial  funnels,   439 
Picric  acid  as  fixing  solution,  25 
as  stain,   45 


Picric  acid  for  fixing  cells,   75 
Picric-nitric    acid    as    a   fixing    solution, 

.25.  ...  . 

Picric-osmic-acetic  acid  solution  as  fixing 

fluid,   25 
Picric-sublimate-osmic  solution  as  fixing 

fluid,   25 
Picrocarmin     as     stain     for     connective 
tissue  in  cartilage,   131 
for    elastic    fibers   in    cartilage,    131 
of  Ranvier,  44 
of  Weigert,  45 
Picrosulphuric    acid    as    fixing   solution, 

25 
Pigment,  97 

cells,   77,   104 

membrane  of  eye,  446,  447,  457 

of  cells,  61 

of  skin,  384 
technic  of,  404 
Pillar  cells,  490 
heads  of,  490 
inner,  490 
outer,  490 
Pilomotor  nerves,  394 
Pineal  gland,  422 

Pituitary  body,  423.     See  also  Hypophy- 
sis. 
Plasma,  blood,   187 

cells,   104 
Plate,  phalangeal,  491,  492 
Platelets,  blood,  fixation  of,  227 
Plates,   technic  for,   235 
Pleura,  visceral  and  parietal  layer  of,  319 
Plexus,   choroid,   439 

epilamellar,  261,  397 

ground,  of  cornea,  451 

Heller's,   283 

hypolamellar,  261 

intracapsular,  429 

myentericus,   286 

of  Auerbach,   286 

of  Meissner,   287 

pericellular,  428 

subepithelial,  of  cornea,  451 

superficial,  of  cornea,  451 
Plicae  palmatae,  356 

semilunares,   282,  473 

sigmoideae,   266 

transversales  recti,   282 
Plural  staining,   44 
Plurifunicular  cells,   408 
Polar  body,    72 

field,    70 

rays,  68 
Polarity  of  cells,  81 

Polygonal   cells   of   cerebral   cortex,    417 
Polykaryocyte,    193 

Polymorphism  of  leucocyte-nucleus,    193 
Polymorphous    cells   of   cerebral    cortex, 

418 
Polynuclear  cells,   70 
Polystratified  cells  of  retina,  464 
Portal  vein,  292 
Posterior  hyaloid  arteries,  468 

vertical  semicircular  canal,   480 


522 


INDEX. 


Potash,  caustic,  as  macerating  solution, 

22 

Potassium  bichromate   and   formalin   as 
fixing  fluid,   27 

chlorate  of,  nitric  acid  and,  as  macerat- 
ing solution,  23 

hydrate,     action     of,     on     connective 
tissue,   128 
Precapillary  arteries,  218 

veins,   220 
Precision  microtome,   TiT, 
Prepuce,  372 
Primary  blastodermic  layers,   79 

egg  tubes  of  Pflüger,  345 

germ  layers,   79 

marrow  spaces,   118 

optic  vesicles,  446 

tendon  bundles,   105 
Primitive  ova,  345,  350 

seminal  cells,  372 
Primordial  ova,  345 
Prisms,  enamel,   238 
Projection  fibers  of  cerebral  cortex,  419 
Prominentia  spiralis,  488 
Pronucleus,  female,   74 

male,   73 
Prophases,  64,  66 
Prostate,  368 

blood-vessels  of,  370 

concretions  of,  370 

corpora  amylacea  of,  370 

nerves  of,  370 

secretion  of,  370 
Prostatic  bodies,  370 
Protoplasm,  58,  59 

of    spermatids,    chromatoid    accessory 
nucleus  of,  377 
sphere  substance  of,  376 
Protoplasmic  currents,   75 

stains,  41 
Protozoa,  58 
Pseudopodia,  60 
Pulp  cords,  204 

splenic,  structure  of,  205 

tooth-,   241 
Pupil,  dilator  muscle  of,  455 

sphincter  muscle  of,   455 
Purkinje' s  cells,    153 

of  cerebellar  cortex,  415 

fibers,   213 

isolated,  demonstration     of,   148 
muscle-cells  of,   147 

vesicle,  344 
Purpurin,  alkaline,  as  stain  for  calcium 

carbonate  in  bone,   132 
Pyloric  glands,  269 
Pyramidal  cells  of  cerebral  cortex,  153 
large,  of  cerebral  cortex,  417 
small,  of  cerebral  cortex,  417 

columns,  crossed,  411 

tract,  direct,  411 
Pyramids  of  Ferrein,  324 

of  Malpighian,  323 


Quintuple   hydroquinon  developer,  51 


Rabl's  hematoxylin-safranin,  46 

solutions,   25 
Rami  cochleares,  494 

vestibuläres,  494 
Ramon  y  Cajal's  technic  for  retina,  475 
Ranvier's  crosses,  demonstration  of,  180 
method  for  examination  of  connective 
tissue,   126 
of  demonstrating  glycogen  in  liver- 
cells,  306 
spaces  in  bone,   132 
of  impregnation,  48 
nodes,   158 

demonstration  of,   180 
picrocarmin,  44 

solution  of  iodin  and  potassium  iodid, 
22 
Recessus  camerae  posterioris,  467 

cochleae,  496 
Rectum,   281 
Red  bone-marrow,   207 

muscles,   141 
Red-blood     corpuscles,     187.     See     also 

Erythrocytes. 
Reissner's  membrane,  485,  489 
Remak's  fibers,    160 

demonstration  of,   182 
Renal  artery,  332 
lobes,  323 
pelvis,  336 
Renflement  biconique,   158 
Respiration,    organs  of,  309 

technic  of,  322 
Respiratory  bronchioles,  313 

elastic    fibers,    demonstration    of,    322 
epithelium,   315 

examination  of,  322 
region,  498 
Resting  nucleus,  63 
Rete  testis,  363 

canals  of,  365 
Retia  mirabilia,   222 

arterial,  333 
Reticular  connective  tissue,  100 
cells  of,   100 
fibers  of  liver,   demonstration  of,   308 
tissue,  demonstration  of,  234 
Reticulum  of  liver,   294 
Retina,  446,   447,  457 
arteries  of,  466 
blood-vessels  of,  465    ' 
central  artery  of,   465 

vein  of,  465 
cone-fibers  of,  459 
externa]    limiting   membrane   of,    459, 

462 
fiber-baskets  of,  462 
ganglion-cell  layer  of,  459,  464 
inferior  nasal  artery  of,  466 
vein  of,  466 
papillary  vein  of,  466 
inner  molecular  layer  of,  464 
nuclear  layer  of,   459,   462 
internal  limiting  membrane  of,  462 
macula  lutea  of,  460 
Müller's  fibers  of,  462 


INDEX. 


523 


Retina,   nerve-fiber  layer  of,  464 

optic  papilla  of,  460 

ora  serrata  of,  461 

outer  fiber  layer  of,  461 

molecular  layer  of,  459,  462 

pars  ciliaris  retinae,  461 
iridica  retinae,   461 

physiologic  excavation  of,  460 

relation  of  elements  of,  to  one  another, 
462 

rod-fibers  of,  458 

superior  nasal  artery  of,  466 
vein  of,  466 
papillary  artery  of,   466 
vein  of,  466 

technic  of,  475 
Retinaculse  cutis,  384 
Retzius,  end-piece  of,  361 

lines  of,  239 
Ring,  contraction-,   158 
Ripart  and  Petit' s  solution,  22 
Ripe  ovum,  350 
Rocking  microtome,  ^^ 
Rod-fibers  of  retina,   458 
Rod-visual  cells,  458 

bipolar  cells  of,  463 
Rolando's  gelatinous  substance,  408 
Root-sheaths     of     hair,    389.    See     also 

Hair,  root-sheaths  of. 
Rose's  carmin-bleu  de  Lyon,  45 
Rouleaux,   187 

Rudder  membrane  of  spermatosome,  361 
Ruffini  end-organ,  388 


Sabin's  modification  of  Mallory's  differ- 
ential stain  for  connective-tissue  fi- 
brillae  and  reticulum,   129 

Sacculus,  481,  482 
ventral,  496 

Saccus  endolymphaticus,  481,  496 

Safranin  as  stain,  44 

Salivary  glands,  253,  255 
blood  supply  of,  259 
nerve  supply  of,   260 

Salts,    lime-,    in    bone,    hematoxylin    as 
stain  for,   132 
isolation  of,   132 

Sarcolemma,   135,   137 

Sarcolytes,   144 

Sarcomeres,   138 

Sarcoplasm,   135,    137 

Sarcous  elements,   141 

Scala  media,  485 
tympani,  485 
vestibuli,  485 

Schachowa's  spiral  segment,  327 

Schlemm's  canal,   448 

Schmidt-Lantermann-Kuhnt's  segments, 
157 

Schmorl's  method  of  staining  bone  cor- 
puscles,  133 

Schräger's  lines,   239 

Schrön's  granule,  344 

Schultze's  iodized  serum,   22 

Schwann,  sheath  of,   158 


Sclera,  446,  448 

blood-vessels  of  449 

nerve  supply  of,  451 

technic  of,  475 
Scleral  conjunctiva,  448 

sulcus,   inner,   449 
Sebaceous  glands,  398 
Secondary  marrow  spaces,   120 

optic  vesicle,  447 

tendon  bundles,   105 
Secretion,  milk,  401 
■   of  intestine,   288 

of  prostate,   370 

process  of,  92 

vacuoles,   291 
Secretory  processes  of  kidney,  335 
Sectioning,   32 
Sections,   21 

staining  of,  41 
Sectionwork,  appropriate  stains  for,  235 
Segmentation  nucleus,   71 
Segments,  Schmidt-Lantermann-Kuhnt's, 

157 
spiral,  of  Schachowa,  327 
Selective  stains,  41 
Semicircular  canal,  483 

anterior  superior  vertical,  480 
external,  480 
horizontal,  480 

posterior  inferior  vertical,  480 
Semilunar  fold,  484 
Seminal  cells,  primitive,  372 
fluid,  examination  of,  378 
vesicles,  368 
Sense  cells,  81 
Sensory  nerve-endings,    166 
encapsulated,    169 
free,   168,   169 
staining  of,   182 
neurone,    peripheral,    diagram  of,    167 
Septa  renis,  324 
Septum  posticum,  438 
Serous  cavities,   224 

gland,   255 
Sertoli's  cells,   364 
Sexual  cells,  fertilization  of,  71 
male,   development  of,   72 
matured,   7 1 
Sharpening  microtome  knife,  37 
Sharpey,  fibers  of,   115 

method  of  isolating,   134 
Sheath,  axial,   176 
Henle's,   162 
medullary,   157 
technic,  440 
Benda's,  442 
Pal's,  442 
Weigert's,  440,  441 
myelin,    157 

of  axial  thread  of  spermatosome,  361 
of  Schwann,    158 
Shedding  hair,   393 

Sihler's  method  of  demonstrating  nerve- 
endings  in  striated  muscle,  184 
Silver  nitrate  as  injection  fluid,  55 
method  of  impregnation,  47 


524 


INDEX. 


Simple  epithelium,  82.     See  also  Epithe- 
lium, simple. 

microscopes,   1 7 
Sinus,  blood,   222 

lactiferus,  400 

lymph-,   199 

pocularis,  370 
Sinuses,   222 
Sinusoids,   221 
Skein,  mother,  67 
Skin,  379 

and  appendages,  379 
technic  of,  403 

glands  of,  396 

lymph-vessels  of,  386 

nerves  of,   387 

pigment  of,  384 
technic  for,  404 

structure  of,  technic  for,  404 

true,  379 

vascular  system  of,  386 
Slide  digestion  for  connective  tissue,  129 
Slides,   20 

Sliding  microtome,  33.     See  also  Micro- 
tome, sliding. 
Small  intestine,  274.     See  also  Intestine, 

small. 
Smell,  organ  of,  498 
Sole  nuclei,   163 

plate,   granular,   163 
Somatic  cell,   71 

Specimens,  permanent,  preparation  of,  52 
Spermatids,   72,  374 

develoment    of,    into    spermatosomes, 

374,  376 

nucleus  of,  377 

protoplasm    of,    chromatoid    accessory 
nucleus  of,  377 
sphere  substance  of,  376 
Spermatoblast,  376 
Spermatocytes,   70,   72 

of  first  order,   374 

of  second  degree,  374 

of  third  degree,  374  ■ 

Spermatogenesis,  372 

schematic  diagrams  of,  373 

technic  of,  378 
Spermatogones,   72 
Spermatogonia,  372 
Spermatosome,  361 

accessory  thread  of,  361 

axial  thread  of,  361 
sheath  of,  361 

development  of,  from  spermatids    374 
376 

flagellum  of,  361 

head  of,  361 

marginal  thread  of,  361 

middle  piece  of,  361 

rudder  membrane  of,  361 

tail  of,  361  • 

terminal  nodule  of,  361 

undulating  membrane  of,  361 
Spermatozoa,  60,   71,   73 
Spermatozoon,    361.     See    also    Sperma- 
tosome. 


Sphere     substance     of     protoplasm     of 

spermatids,  376 
Sphincter  muscle  of  pupil,  455 
Spider  cells,  435 
Spinal  cord,  406 

anterior  median  fissure  of,  406 
commissures  of,  412 
gray  substance  of,  406,  409 
horns  of,   408 

posterior  median  septum  of,  406 
white  substance  of,  406,  409 
ganglia,  424 

ganglion  cell  of  Dogiel,  426 
Spindle,  achromatic,  68 

central,   68 
Spindle-shaped   cells  of  cerebral  cortex 

4^7 
Spiral  ganglion  of  cochlea,  494 

organ  of  Corti,  489 

segment  of  Schachowa,  327 
Spirem,  67 
Spleen,   202 

blood  supply  of,   203 

lobules,   204 

diagram  of,  205 

trabeculae  of,   203 
Splenic  pulp,  structure  of,  206 

tissue,  demonstration  of,  234 
Splenolymph  glands,  201 
Spongioblasts,  434 

diffuse,  464 

stratum,  464 
Spongioplasm,  60,   274 
Spot,  Wagner's,  344 
Staining,  41 

blood-cells,   227 

blood  films,  Wright's  method,  229 

bone    corpuscles,    Schmorl's    methodj 

133 
double,  44 

of  cells,   76 
fibers  of  olfactory  nerve,  182 
in  bulk,  46 

diagram  for,  47 
in  sections,  diagram  for,  47 
motor  nerve-endings,   182 
neurofibrils    and    Golgi-nets,     Bethe's 

method,  443 
neuroglia,  444 

fibers,  Benda's  method,  445 
Mallory's  methods,  445 
plural,  44 
section,  41 

sensorv  nerve-endings,   182 
Stains,  41 
acid,  41 

fuchsin-picric     acid      solution,     van 
Gieson's,  45 

hem  alum,   43 
alkaline  purpurin,  for  calcium  carbon- 
ate in  bone,   132 
alum-carmin,  42 

for  bulk,  46 
anilin,  44 
basic,  41 
Biondi-Heidenhain  triple,  46 


INDEX. 


525 


Stains,  Bismarck  brown,  44 
borax-carmin,  alcoholic,  41 
for  bulk,  46 
aqueous,  41 
carmin,  41 

carmin-bleu  de  Lyon,  45 
coal-tar,  44 

Czocor's  cochineal  solution,  42 
differential,     for    connective-tissue    fi- 

brillae  and  reticulum,   128 
EhrUch's  methylene-blue,   for  nervous 

tissues,   182 
eosin,  for  blood-cells,   227 
for  adipose  tissue,   130 
for  canaUcular  system  in  cartilage,  131 
for  mucin,  305 
for  sectionwork,   235 
fuchsin-resorcin  elastic  fibers,  128 
gold  chlorid,  for  capsules  of  cartilage, 

131 
Heidenhain's  iron,  for  bulk,  46 
hemalum,  43 
acid,  43 
for  bulk,  46 
hematoxylin,  Böhmer's,  42 
for  bulk,  46 
Delafield's,  43 
EhrKch's,  43 

for  nuclei  and  granules,   228 
for  lime-salts  in  bone,   132 
Friedländer' s  glycerin-,  43 
hematoxylin-eosin,   45 
hematoxyhn-safranin,  46 
hematoxylon,  42 

Heidenhain's  iron,  43 
iodo-iodid  of  potassium,  to  demonstrate 

glycogen  in  cartilage,   131 
magenta  red,  for  connective  tissue,  128 
methylene-blue,  for  nerve-fibers,  184 
methyl-green,  44 
nuclear,  41 

orcein,  for  connective  tissue,  128 
paracarmin,  42 
for  bulk,  46 
Partsch's  cochineal  solution,  42 
picric  acid,  45 
picrocarmin,  Ranvier's,  44 

Weigert's,  45 
protoplasmic,   41 
safranin,  44 
selective,  41 
Sudan  III,  for  fat,   130 
triple,   46 
Stars,  daughter,  374 
Stellate  cells  of  cerebellar  cortex,  415 
large,  of  cerebellar  cortex,  416 
of  cerebral  cortex,  417 
of  liver,   295 
Stellulse  vasculosae,  453 
Steno's  ducts,   253 
Stomach,   264,   266 
blood-vessels  of,   284 
crypts  of,   266 

epitheUum     and     secretory     cells     of, 
changes    in,    during    secretion,    27T 
foveolae  of,   266 


Stomach,  glands  of,   267 
cardiac,   267 
fundus,  268 
pyloric,   269 
mucous  membrane  of,   266 

fixation  of,  305 
muscularis  mucosae  of,   271 
Stomach-pits,  266 
Straight  tubules  of  testes,  363 
Stratified  epithehum,  83.   See  also  Epithe- 
lium, stratified. 
Stratum  circulare,  477 
of  intestine,  266 
corneum,  379,  381 
fibrosum  of  intestine,   265 
germinativum,  379 
granulosum,  379 
of  ovary,  347 
longitudinale  of  intestine,  266 
lucidum,  381 

technic  for,  403 
Malpighii,  379 

technic  of,  403 
proprium  of  oral  cavity,  236 
radiatum,  477 
spongioblasts,   464 
submucosum  of  oral  cavity,  236 
Stria  vascularis,  488 
Striated  muscle,    nerve-endings  in,    Sih- 
ler's  method  of  demonstrating,    184 
muscle-fibers,  technic  of,   147 
muscular  tissue,  blood-vessels  in,   143 
Striation  of  Baillarger,  421 
of  Bechtereff  and  Kaes,  421 
of  iris,  455 
of  ovary,  344 

of  red  blood-corpuscles,   187 
Subarachnoid  space,  437 
Subdural  space,  437 
Subepithelial  plexus  of  cornea,  451 
Subhngual  gland,  255 
Submaxillary  gland,  258 
Submucosa  of  intestine,  265 
of  oral  cavity,   236 
of  urethra,  372 
Substantia  propria  of  cornea,  449 

technic  for,  474 
Succus  prostaticus,  370 
Sudan  III  as  stain  for  fat,   130 
Sudoriparous  glands,  396.  See  also  Sweat- 

glands. 
Sulcus  of  matrix  of  nail,  394 

spiralis  internus,  487 
Sulphuric  acid  as  macerating  solution,  23 
Superficial  plexus  of  cornea,  45 1 
Superior  nasal  artery  of  retina,  466 
vein  of  retina,  466 
papillary  artery  of  retina,  466 
vein  of  retina,  466 
Suprarenal    capsule,    demonstration    of, 

343 
glands,  339 

blood-vessels  of,  341 

nerves  of,  342 
Suspensory  ligament  of  lens,  467 
Sustentacular    cells,    92,    250,    372,    483 


526 


INDEX. 


Sus tentacular  fiber    492 
Sweat-glands,  396 

capillaries  of,  397 

coiled  portion  of,  396 

modified,  398 

nerves  of,  397 
Sympathetic  ganglia,  427 
Syncytium,  97 

development  and  differentiation,  98 


Tactile  corpuscles,  Meissner' s,  387 
technic  of,  405 

menisci,  387 
technic  of,  405 

papilla;,  383 
Taenice  coli,   266 

semilunares,  282 
Tannic    acid,    effect    on    red    blood-cor- 
puscles,  189 
Tapetum  cellulosum,  453 

fibrosum    453 
Tarsal  gland,   472 
Taste-buds,  249 

nerves  in,  demonstration  of,  304 

technic  for,  303 
Taste-pore,  250 
Teasing,   2 1 
Teeth,   238 

adult,  structure  of    238 

auditory,  488 

blood-vessels  of,  242 

development  of,  243 
method  of  studying,  303 

medullated  nerve-fibers  of,   242 

pulp  of,   241 

technic  for,  303 
Teichmann' s  crystals,   188 

method  of  obtaining,  230 
Tela  submucosa,  236 
Tellyesnicky's  fluid,  26 
Telodendria,   150,   162 
Telolemma  nuclei,   163 
Telophases,   65,   70 

Temperature,  high,  effect  on  tissues,  29 
Temporal  artery,  inferior,  of  retina,  466 
superior,  of  retina,  466 

vein,  inferior,  of  retina,  466 
superior   of  retina,  466 
Tendon,   105 

and    muscle,    relation    of,    method    of 
studying,    148 

bundles,   primary,    105 
secondary,   105 

cells  from  tail  of  rat,  107 

fasciculi,   105 
Tenon's  capsule,  448 
Terminal  bronchioles,  314,  315 

fibers  of  cerebral  cotex,  420 

ledges,  86 

nodule  of  spermatosome,  361 
Testes,  362 

blood-vessels  of,  367 

convoluted  tubules  of,  363 

examination  of,  378 

lymph-vessels  of,  367 


Tests,  nerves  of,  367 
straight  tubules  of,  363 
vasa  efferentia  of,  363,  365 
Theca  folliculi,  347 
Third  eyelid,  473 
Thoma's  ampullae,   204 

Zwischenstück,   204 
Thoma-Zeiss  hemocytometer,  232 
Thread-granules,  60 
Thrombocytes,   194 
Thymus  gland,   210 

blood  supply  of,  212 
Thyroid  gland,  319 

acini  of,  chief  cells  of,  320 

colloid  cells  of,  320 
blood  supply  of,  320 
demonstration  of,  322 
nerves  of,  320 
granules,   149 
Tissue,   79 
adipose,   107 

stain  for,    130 
connective,    96.     See    also    Connective 

tissue. 
effect  of  high  temperature  on,  29 
elastic,   effect  of  trypsin  digestion  on, 
127 
method  of  obtaining,  127 
epithelial,  80 
erectile,  371 
fibrous,  elastic,   106 
liver,  technic  of,  307 
lymphoid,   196 
mesenchymatous,  97 
muscular,   134 

destruction  of,   144 
development  of,   144 
heart,  development  of,   146 
nerve-fibers  ending  in,   162 
striated,  blood-vessels  in,   143 
technic  of,   147 
nervous,   148 

Ehrlich's   methvlene-blue   stain   for, 

182 
fixation  of,   183 
technic  of,   180 
ovarian,  fixation  of,  378 
pulmonary,  demonstration  of,  322 
reticular,  demonstration  of,  234 
splenic,  demonstration  of,  234 
Toison's  fluid  for  diluting  blood,  232 
Tomes'  granular  layer,  246 

processes,   244 
Tongue,   247 

lymph-follicles  of,   251 
mucous  membrane  of,   247 
nerve  supply  of,   252 
papillae  of,   247 
Tonsils,   lymph-follicles  of,  251 

pharyngeal,   251 
Trabeculae  of  liver,  290 
of  lymph-glands,   198 
of  spleen,   203 
Trachea,  310 

demonstration  of,  322 
nerves  of,  311 


INDEX. 


527 


Transitional  epithelium,  85 

leucocytes,   192 
Triple  stains,  46 
Trophoplasts,  385 
Trypsin   digestion,    effect   on   connective 

and  elastic  tissues,  127 
Tubular  glands,  89 
coiled,  90 

compound  branched,  90 
reticulated,  90 
simple  branched,  90 
Tubules,  convoluted,  of  testes,  363 
dentinal,   240 

intermediate,  of  pancreas,  300 
of  kidney,  demonstration  of,  342 
straight  collecting,  of  kidney,  323 

of  testes,  363 
uriniferous,  323 

membrana  propria  of,  330 
Tubuli  recti,  363 
Tubulo-alveolar  gland,  90 
Tunica  albuginea,  92,  344,  362 
dartos,  384 
externa  of  eye,  446 
fibrosa  of  eye,  446,  448 
interna  of  eye,  446,  457 
mucosa  of  intestine,  265 
propria  of  oral  cavity,  236 
sclerotica,  446,  448.     See  also  Sclera. 
vaginalis,  362 
vasculosa,  362 
of  eye,  446,  452 
Tunics  of  eye,  446 
Tunnel-fibers,  494 
Tympanic  investing  layer,  489 
membrane,  476 

cutaneous  layer  of,  476 

epidermis  of,  476 
lamina  propria  of,  477 
mucous  layer  of,  47^ 
Tympanum,  478 
Tyson,  glands  of,  372 


Undecalcified  bone,  microscopic  prep- 
arations of,   131 
Undulating  membrane  of  spermatosome, 

361 
Unicellular  glands,  87 
Unna's  orcein  stain  for  connective  tissue, 

128 
Ureter,  336 

nerves  of,  339 

technic  of,  343 
Urethra,  epithelium  of,  371 

submucosa  of,  372 
Urinary  organs,  323 
Uriniferous  tubules,  323 

membrana  propria  of,  330 
Uterus,  355 

blood  supply  of,   357 

lymphatics  of,  357 

mucous  membrane  of,  355 

muscular  coat  of,  356 

nerves  of,  358 
Utriculosaccular  duct,  481 


Utriculus,  481,  482 
dorsal,  496 
nerve-fibers  of,  483 
wall  of,  482 


Vacuole  of  ovum,  344 
Vacuoles,  61 

secretion,   291 
Vagina,  358 

mucous  membrane  of,  358 
epithelium  of,   358 

muscular  coat  of,  359 

nerves  of,  360 

vestibule  of,  epithelium  of,  360 
Valves,  auriculoventricular,  of  heart,  213 

of  veins,   220 
Valvulae  conniventes,  265,  274 
Van    Gieson's    acid    fuchsin-picric    acid 

solution,  45 
Vas  aberrans  Halleri,  366 

deferens,  367 

epididymitis,  364,  366 

Spirale,  489 
Vasa  afferentia,    197 
of  kidney,  332 

efferentia,   197 

of  testes,  363,  365 

recta  spuria,  334 
Vascular  canals,   112 

papilla;,  383 

supply  of  larynx,  310 

system,   213 
of  skin,  386 

tunic  of  eye,  446,  452 
Vater-Pacinian  corpuscles,  1 73 

distribution  of,   174 
Veins,   219 

central,  of  retina,  465 

interlobular,  of  kidney,  334 
of  Hver,   293 

nasal,  inferior,  of  retina,  466 
superior,  of  retina,  466 

papillary,  inferior,  of  retina,  466 
superior,  of  retina,  466 

portal,   292 

precapillary,   220 

small,   220 

temporal,  inferior,  of  retina,  466 
superior,  of  retina,  466 

valves  of,   220 
Venae  arciformes,  334 

stellatae,  334 

vorticosas,  452 
Ventral  sacculus,  496 
Ventrolateral  column,  408 
Ventromesial  column,  408 
Venulae  rectfe,  334 

Vermiform  appendix,  mucosa  of,  lymph- 
follicles  of,   281 
Vesicles,  germinal,   71 

optic,  primary,  446 
secondary,  447 

Purkinje's,   344 

seminal,  368 

(Reissner's),  485,  489 


1^28 


INDEX. 


Vestibule  of  ear,  480 

of  nasal  cavity,  498 

of  vagina,  epithelium  of,  360 
Villi  of  mucous  membrane  of  small  in- 
testine,  274 

of  small  intestine,  lacteals  of,  285 
Virchow's    bone    corpuscles,    method    of 

isolating,   134 
Visual  cells,  458 
Vitreous  body,  446,  467 

hyaloid  membrane  of,  467 

membrane,  452,  453 
Volkmann' s  canals,   115 
vom  Rath's  solutions,   25 
von   Ebner's   method   of   decalcification, 

von  Koch's  technic  for  bone,   132 


Wagner's  spot,  344 
Wandering  cells,  60,   103,   104 
Water,     distilled,     for     fixing     paraffin 
sections  to  slide,  39 
effect    on    red    blood-corpuscles,     188 
Wax  plates,  56 

apparatus  for  making,  56 
reconstruction  by,  55 
Bom's  method,  56 
cutting    out    parts    to    be   recon- 
structed, and  completing  model, 

57. 
drawing  apparatus,  56 

serial  sections,  56 

Weigert's    fuchsin-resorcin  elastic   fibers 

stain,   128 


Weigert's  methods  for  demonstration  of 
medullary  sheath,  440,  441 

picrocarmin,  45 
Wharton's  ducts;   253,  254 

jelly,   100 
White   blood-corpuscles,    191.     See   also 
Leucocytes. 

fibers,  99 

fibrocartilage,   no 

muscles,   141 

rami  communicantes,  429 
fibers,  429,  456 

substance  of  spinal  cord,  406,  409 
Wirsungian  duct,  298 
Wolffian  duct,  360 
Wright's     method     of     staining     blood 

films,   229 
Wrisberg,  cartilages  of,  310 


Yellow^  bone-marrow,  207,  210 
gelatin  mass  as  injection  fluid,  54 


Zenker's  fluid,  26 
Zinn's  arterial  circle,  465 

zonule,  467 
Zona  pellucida,  origin  of,  350 
Zone,  boundary,  of  choroid,  453 

marginal,   81 
Zonula  ciliaris,  446,  467 
Zonule  of  Zinn,  467 
Zymogen,   255 

granules   in    pancreas,  demonstrating, 
308 


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Cabot's 
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Diseases  of  the  Stomach,  Intestines,  and  Pancreas.     By  Robert 
Coleman  Kemp,  M.  D.,  Professor  of  Gastro-intestinal  Diseases  at  the 
New  York  School  of  Clinical    Medicine.     Octavo  of  1021   pages,  with 
388  illustrations.     Cloth,  ^6.50  net ;  Half  Morocco,  ;$8.oo  net. 
JUST  READY— NEW  (2d)  EDITION 

The  new  edition  of  Dr.  Kemp's  successful  work  appears  after  a  most  search- 
ing revision.  Several  new  subjects  have  been  introduced,  notably  chapters  on 
Colon  Bacillus  Infection  and  on  Diseases  of  the  Pattcreas,  the  latter  article  being 
really  an  exhaustive  monograph,  covering  over  one  hundred  pages.  The  section 
on  Duodenal  Ulcer  has  been  entirely  rewritten.  Visceral  Displacements  are  given 
special  consideration,  in  every  case  giving  definite  indications  for  surgical  inter- 
vention when  deemed  advisable.  There  are  also  important  chapters  on  the  Intes- 
tinal Complications  of  Typhoid  Fever  and  on  Diverticulitis. 

The  Therapeutic  Gazette 

"The  therapeutic  advice  which  is  given  is  excellent.  Methods  of  physical  and  clinical 
examination  are  adequately  and  correctly  described." 


Deaderick    on     Malaria 

Practical  Study  of  Malaria.  By  William  H.  Deaderick,  M.  D., 
Member  American  Society  of  Tropical  Medicine;  Fellow  London 
Society  of  Tropical  Medicine  and  Hygiene.  Octavo  of  402  pages, 
illustrated.     Cloth,  ;^4.50  net;  Half  Morocco,  ^6.00  net. 

Frank  A.  Jones,    M.  D.,  Memphis  Hospital  Medical  College. 

"We  have  been  waiting  for  many  years  for  such  a  work  written  by  a  man  who  sees  malaria 
in  all  its  forms  in  a  highly  malarious  climate." 


Two  Printings 
in  Six  Months 


Niles  on  Pellagra 

Pellagra.  By  George  M.  Niles,  M.  D.,  Professor  of  Gastro- 
enterology and  Therapeutics,  Atlanta  School  of  Medicine.  Octavo  of 
253  pages,  illustrated.     Cloth,  ^^3.00  net. 

This  is  a  book  you  must  have  to  get  in  touch  with  the  latest  advances  con- 
cerning this  disease.  It  is  the  first  book  on  the  subject  by  an  American  author, 
and  the  first  in  any  language  adequately  covering  diagnosis  and  trcatmoit. 
Pathology,  heretofore  an  echo  of  European  views  only,  is  here  presented  from  an 
American  point  of  view  as  well,  much  original  work  being  included.  The  clinical 
description  covers  the  manifestations  of  Pellagra  from  every  angle. 


SAUNDERS'    BOOKS   ON 


Tousey*s 

Medical  E^lectricity  and  X-Kays 

Medical  Electricity  and  the  X=Rays.  By  Sinclair  Tousey,  M.  D., 
Consulting  Surgeon  to  St.  Bartholomew's  Hospital,  New  York.  Octavo 
of  1116  pages,  with  750  practical  illustrations,  16  in  colors. 

Cloth,  ;^7.oo  net ;  Half  Morocco,  1^8.50  net. 

FOR  THE  PRACTITIONER 

Written  primarily  for  the  general  practitioner,  this  book  gives  just  the 
information  he  wishes  to  have  regarding  the  use  of  medical  electricity,  the  thera- 
peutic results  obtained,  etc.  At  the  same  time  it  tells  the  specialist  how  the  most 
eminent  electrotherapeutists  are  securing  results.  The  work  gives  explicit  di- 
rections for  the  care  and  regulation  of  static  machines,  .r-ray  tubes,  and  all 
apparatus.  It  tells  how  to  make  x-ray  pictures  by  a  practical  technic  easily  fol- 
lowed.     Dental  7-adiograpJiy  the  author  has  made  his  own. 

The  Military  Surgeon 

"The  whole  subject  of  medical  and  surgical  electricity  is  covered  in  these  pages.  Not 
only  is  it  covered,  but  in  great  detail." 

McKenzie  on  Exercise  in 
Education   and    Medicine 

Exercise  in  Education  and  Medicine.  By  R.  Tait  McKenzie,  B.  A., 
M.  D.,  Professor  of  Physical  Education  and  Director  of  the  Department, 
University  of  Pennsylvania.  Octavo  of  393  pages,  with  346  original 
illustrations.  Cloth,  $3.50  net. 

D.  A.  Sargeant,  M.   D.,  Director  of  Hemenway  Gymnasium,  Harvard  Uni'^ersity. 

"  It  cannot  fail  to  be  helpful  to  practitioners  in  medicine.  The  classification  of  athletic 
games  and  exercises  in  tabular  form  for  different  ages,  sexes,  and  occupations  is  the  work  of  an 
expert.     It  should  be  in  the  hands  of  every  physical  educator  and  medical  practitioner." 

Bonney's  Tuberculosis  second  Edition 

Tuberculosis.  By  Sherman  G.  Bonney,  M.  D.,  Professor  of  Medi- 
cine, Denver  and  Gross  College  of  Medicine.  Octavo  of  955  pages,  with 
243  illustrations.      Cloth,  ^7.00  net;   Half  Morocco,  1^8.50  net. 

Maryland  Medical  Journal 

"  Dr.  Bonney's  book  is  one  of  the  best  and  most  exact  works  on  tuberculosis,  in  all  its 
aspects,  that  has  yet  been  published." 


THE  PRACTICE    OF  MEDICINE 


Anders* 
Practice   of  Medicine 


A  Text=Book  of  the  Practice  of  Medicine.  By  James  M.  Anders, 
M.  D.,  Ph.  D.,  LL.  D.,  Professor  of  the  Practice  of  Medicine  and  of 
Clinical  Medicine,  Medico-Chirurgical  College,  Philadelphia.  Hand- 
some octavo,  1326  pages,  fully  illustrated.  Cloth,  ^5.50  net;  Half 
Morocco,  ^7.00  net. 

THE  NEW  (10th)  EDITION 

The  success  of  this  work  is  no  doubt  due  to  the  extensive  consideration  given 
to  Diagnosis  and  Treatment,  under  Differential  Diagnosis  the  points  of  distinction 
of  simulating  diseases  being  presented  in  tabular  form.  In  this  new  edition 
Dr.  Anders  has  included  all  the  most  important  advances  in  medicine,  keeping 
the  book  within  bounds  by  a  judicious  elimination  of  obsolete  matter.  A  great 
many  articles  have  also  been  rewritten. 

Wm.  E.  Quine,  M.  D., 

Professor  of  Medicine  and  Clinical  Medicine,  College  of  Physicians  and  Surgeons,  Chicago. 
"  I  consider  Anders'  Practice  one  of  the  best  single-volume  works  before  the  profession  at 
this  time,  and  one  of  the  best  text-books  for  medical  students." 


DaCosta's  Physical  Diagnosis 

Physical  Diagnosis.  By  John  C.  DaCosta,  Jr.,  M.  D.,  Associate 
in  Clinical  Medicine,  Jefferson  Medical  College,  Philadelphia.  Octavo 
of  557  pages,  with  225  original  illustrations.     Cloth,  ^3.50  net. 

NEW  (2d)  EDITION 

Dr.  DaCosta' s  work  is  a  thoroughly  new  and  original  one.  Every  method 
given  has  been  carefully  tested  and  proved  of  value  by  the  author  himself. 
Normal  physical  signs  are  explained  in  detail  in  order  to  aid  the  diagnostician  in 
determining  the  abnormal.  Both  direct  and  differential  diagnosis  are  emphasized. 
The  cardinal  methods  of  examination  are  supplemented  by  full  descriptions  of 
technic  and  the  clinical  utility  of  certain  instrumental  means  of  research. 

Dr.  Henry  L.  Eisner,  Professor  of  Medicine  at  Syracuse  University. 

"  I  have  reviewed  this  book,  and  am  thoroughly  convinced  that  it  is  one  of  the  best  ever 
written  on  this  subject.     In  every  way  I  find  it  a  superior  production." 


SAUNDERS'  BOOKS  ON 


Sahli*s  Diagnostic  Methods 

A  Treatise  on  Diagnostic  Methods  of  Examination.  By  Prof. 
Dr.  H.  Sahli,  of  Bern.  Edited,  with  additions,  by  Nath'l  Bowditch 
Potter,  M.  D.,  Assistant  Professor  of  Clinical  Medicine,  Columbia  Uni- 
versity (College  of  Physicians  and  Surgeons),  New  York.  Octavo  of 
1229  pages,  illustrated.     Cloth,  $6.^0  net ;  Half  Morocco,  |8.oo  net. 

THE  NEW  (2d)  EDITION,  ENLARGED  AND  RESET 

Dr.  Sahli' s  great  work  is  a  practical  diagnosis,  written  and  edited  by  practical 
clinicians.  So  thorough  has  been  the  revision  for  this  edition  that  it  was  found 
necessary  practically  to  reset  the  entire  work.  Every  line  has  received  careful 
scrutiny,  adding  new  matter,  eliminating  the  old. 

Lewellys  F.  Barker,  M.  D. 

Professor  of  the  Principles  and  Practice  of  Medicine,  Johns  Hopkins  University 
"  I  am  delighted  with  it,  and  it  will  be  a  pleasure  to  recommend  it  to  our  students  in  the 
Johns  Hopkins  Medical  School." 

Friedenwald  and  Ruhrah  on  Diet 

Diet  in  Health  and  Disease.     By   Julius    Friedenwald,    M.  D., 
Professor  of  Diseases  of  the  Stomach,  and  John  Ruhrah,  M.  D.,  Pro- 
fessor of  Diseases  of  Children,  College  of  Physicians  and  Surgeons, 
Baltimore.     Octavo  of  764  pages.     Cloth,  ;^4.oo  net. 
THE  NEW  (3d)   EDITION 

This  new  edition  has  been  carefully  revised,  making  it  still  more  useful  than  the  two 
editions  previously  exhausted.  The  articles  on  milk  and  alcohol  have  been  rewritten,  additions 
made  to  those  on  tuberculosis,  the  salt-free  diet,  and  rectal  feeding,  and  several  tables  added, 
including  Winton's,  showing  the  composition  of  diabetic  foods. 

George  Dock.  M.  D. 

Professor  of  Theory  and  Practice  and  of  Clinical  Medicine,    Tulane   University. 
"  It  seems  to  me  that  you  have  prepared  the  most  valuable  work  of  the  kind  now  available. 
I  am  especially  glad  to  see  the  long  list  of  analyses  of  different  ki^ds  of  foods." 

Carter's  Diet  Lists  J"**  R«*^y 

Diet  Lists  of  the  Presbyterian  Hospital  of  New  York  City. 
Compiled,  with  notes,  by  Herbert  S.  Carter,  M.  D.  i2mo  of  129 
pages. 

Here  Dr.  Carter  has  compiled  all  the  diet  lists  for  the  various  diseases  and  for  conva- 
lescence as  prescribed  at  the  Presbyterian  Hospital.     Recipes  are  also  included. 


PRACTICE    OF  MEDICINE 


Oertel  on  Bri^ht*s  Disease 

The  Anatomic   Histological   Processes  of    Bright's  Disease. — By 

Horst  Oertel,  M.  D.,  Director  of  the  Russell  Sage  Institute  of 
Pathology,  New  York.  Octavo  of  227  pages,  with  44  illustrations  and 
6  colored  plates.     Cloth,  ;^5.oo  net;  Half  Morocco,  %6.^o  net. 

ILLUSTRATED 

These  lectures  deal  with  the  anatomic  histological  processes  of  Bright's 
disease,  and  in  a  somewhat  different  way  from  the  usual  manner.  Everywhere 
relations  are  emphasized  and  an  endeavor  made  to  reconstruct  the  whole  as  a 
unit  of  interwoven  processes. 

The  Lancet,  London 

"Dr.  Oertel  gives  a  clear  and  intelligent  idea  of  nephritis  as  a  continuous  process.  We 
can  strongly  recommend  this  book  as  thoughtful,  scientific,  and  suggestive." 


Fenwick  on  Dyspepsia 

Dyspepsia By  William  Soltau  Fenwick,  M.  D.,  of  London, 

England.     Octavo  volume  of  485  pages,  illustrated.     Cloth,  1^3.00  net. 

Dr.  Fenwick  takes  up  this  important  disease  in  a  thoroughly  systematic  way. 
He  discusses  the  causes,  pathology,  symptoms,  diagnosis,  prognosis,  and  treat- 
ment with  a  clearness,  a  definiteness,  and,  withal,  a  conciseness  that  makes  his 
work  the  most  practical  and  useful  on  this  subject. 

Southern  Medical  Journal 

"  The  suggestions  on  treatment  are  logical  and  practical,  being  particularly  helpful  in 
many  of  those  perplexing  types  so  often  encountered." 


Smith's  What  to  Eat  and  Why 

What  to  Eat  and  Why.  By  G.  Carroll  Smith,  M.D.,  Boston. 
l2mo  of  312  pages.     Cloth,  ;^2.5o  net. 

FOR  THE  PRACTITIONER 

With  this  book  you  no  longer  need  send  your  patients  to  a  specialist  to  be 
dieted — you  will  be  able  to  prescribe  the  suitable  diet  yourself  just  as  you  do 
other  forms  of  therapy.  Dr.  Smith  gives  '  •  the  why  ' '  of  each  statement  he 
makes.  It  is  this  knowing  why  which  gives  you  confidence  in  the  book,  which 
makes  you  feel  that  Dr.  Smith  knows. 

Slade's  Physical  Examination  and  Dia£[nostic  Anatomy 

Physical  Examination  and  Diagnostic  Anatomy. — By  Charles  B.  Slade,  M.D., 
Chief  of  Clinic  in  General  Medicine,  University  and  Bellevue  Hospital  Medical  College. 
i2mo  of  146  pages,  illustrated.     Cloth,  ^1.25  net. 

"In  this  volume  is  contained  the  fundamental  methods  and  principles  of  physical  examination,  well 
illustrated,  largely  by  line  drawings.  The  book  is  to  be  strongly  recommended." — Boston  Medical  ana 
Surgical  Jon  mal. 


SAUNDERS'  BOOKS  ON 


AMERICAN  EDITION 

Nothnagels  Practice 

UNDER   THE   EDITORIAL    SUPERVISION  OF 

ALFRED   STENGEL.   M.D. 

Professor  of  Medicine  in  the  University  of  Pennsylvania 


Typhoid  and  Typhus  Fevers 

By  Dr.  H.  Curschmann,  of  Leipsic.  Edited,  with  additions,  by  William 
Osler,  M.  D.,  F.  R.  C.  P.,  Regius  Professor  of  Medicine,  Oxford  University, 
Oxford,  England.     Octavo  of  646  pages,  illustrated. 

Smallpox  (including  Vaccination),  Varicella,  Cholera  Asiatica, 
Cholera  Nostras,  Erysipelas,  Erysipeloid,  Pertussis,  and 
Hay  Fever 

By  Dr.  H.  Immermann,  of  Basle  ;  Dr.  Th.  von  Jürgensen,  of  Tübingen  ; 
Dr.  C.  Liebermeister,  of  Tübingen ;  Dr.  H.  Lenhartz,  of  Hamburg ; 
and  Dr.  G.  Sticker,  of  Giessen.  The  entire  volume  edited,  with  additions, 
by  Sir  J.  W.  Moore,  M.  D.,  F.  R.  C.  P.  I.,  Professor  of  Practice,  Royal  Col- 
lege of  Surgeons,  Ireland.     Octavo  of  682  pages,  illustrated. 

Diphtheria,  Measles,  Scarlet  Fever,  and  Röthein 

By  William  P.  Northrup,  M.  D.,  of  New  York,  and  Dr.  Th.  von  Jür- 
gensen, of  Tübingen.  The  entire  volume  edited,  with  additions,  by  William 
P.  Northrup,  M.  D.,  Professor  of  Pediatrics,  University  and  Bellevue  Hos- 
pital Medical  College,  New  York.  Octavo  of  672  pages,  illustrated,  including 
24  full-page  plates,  3  in  colors. 

Diseases  of  the  Bronchi,  Diseases  of  the  Pleura,  and  Inflam» 
mations  of  the  Lungs 

By  Dr.  F.  A.  Hoffmann,  of  Leipsic ;  Dr.  O.  Rosenbach,  of  Berhn ;  and 
Dr.  F.  Aufrecht,  of  Magdeburg.  The  entire  volume  edited,  with  additions, 
by  John  H.  Musser,  M.  D.,  University  of  Pennsylvania.  Octavo  of  1029 
pages,  illustrated,  including  7  full-page  colored  lithographic  plates. 

Diseases  of  the  Pancreas,  Suprarenals,  and  Liver 

By  Dr.  L.  Oser,  of  Vienna  ;  Dr.  E.  Neusser,  of  Vienna  ;  and  Drs.  H. 
Quincke  and  G.  Hoppe-Seyler,  of  Kiel.  The  entire  volume  edited,  with 
additions,  by  Reginald  H.  Fritz,  A.  M.,  M.  D.,  Hersey  Professor  of  the 
Theory  and  Practice  of  Physic,  Harvard  University  ;  and  Frederick  A. 
Packard,  M.  D.,  Late  Physician  to  the  Pennsylvania  and  Children's  Hos- 
pitals, Philadelphia.      Octavo  of  918  pages,  illustrated. 

SOLD  SEPARATELY— PER  VOLUME :  CLOTH,  $5.00  NET ;    HALF  MOROCCO,  $6.00  NET 


PRACTICE    OF  MEDICINE  1 1 


AMERICAN   EDITION 

NOTHNAGEL'S  PRACTICE 

Diseases  of  the  Stomach  ,     .,      ,,  u    r„APTP<;  r 

Bv  Dr  F  Riegel,  of  Giessen.  Edited,  with  additions,  by  Charles  G 
STOCKTON.  MD.,  Professor  of  Medicine,  University  of  Buffalo.  Octavo  of 
835  pages,  with  29  text-cuts  and  6  full-page  plates. 

Diseases  of  the  Intestines  and  Peritoneum  Second  Edition 

Bv  DR.  Hermann  Nothnagel,  of  Vienna.  Edited,  with  addiüons  by 
H.  D.  ROLLESTON,  M.  D.,  F.  R.  C  P.,  Physician  to  St.  George  s  Hospital. 
London.      Octavo  of  1 100  pages,  illustrated. 

Tuberculosis  and  Acute  General  Miliary  Tuberculosis 

Bv  Dr    G    Cornet    of  Berlin.     Edited,   with  additions,  by  Walter  B. 
James,  m'.  D.',  Professor  of  the  Practice  of  Medicine,   Columbia  University, 
New  York.     Octavo  of  806  pages. 
Diseases  of  the  Blood   {Anemia,  chlorosis,  Leukemia,  and  Pseudoleukemia) 

Bv  Dr  p.  Ehrlich,  of  Frankfort-on-the-Main  ;  Dr.  A.  Lazarus,  of  Char- 
lottenburg-  Dr.  K.  von  Noorden,  of  Frankfort-on-the-Main  ;  and  Dr. 
Felix  PiNKUS,  of  Berlin.  The  entire  volume  edited,  with  additions,  by  Alfred 
Stengel  M  D..  Professor  of  Medicine,  University  of  Pennsylvania.  Octavo 
of  714  pages,  with  text-cuts  and  13  full-page  plates,  5  in  colors. 

Malarial  Diseases.  Influenza,  and  Dengue  .r  wn. 

By  DR.  J.  MANNABERG,  of  Vienna,  and  Dr.  O.  Leichtenstern  of  Cologne. 
The  entire  volume  edited,  with  additions,  by  Ronald  Ross,  F.  R  C.  S.  (EngO, 
F  R  S  Professor  of  Tropical  Medicine,  Umversity  of  Liverpool  ;  J  \\  .  W  • 
Stephens,  M.  D.,  D.  P.  H.,  Walter  Myers  Lecturer  on  Tropical  Medicine 
University  of  Liverpool  ;  and  Albert  S.  Grunbaum,  F.  R.  C.  P.,  lessor 
of  Experimental  Medicine,  University  of  Liverpool.  Octavo  of  769  pages, 
illustrated.  .     »%.   xt. 

Diseases  of  Kidneys  and  Spleen,  and  Hemorrhagic  Diatheses 

By  Dr.  H.  Senator,  of  Berhn,  and  Dr.  M.  Litten  of  Berhn.  The  entire 
volume  edited,  with  additions,  by  James  B.  Herrick,  M.  D..  Professo  of  the 
Practice  of  Medicine,  Rush  Medical  College.     Octavo  of  815  pages,  illust. 

Diseases  of  the  Heart  t^„   t    1.«,.», 

Bv  Prof    Dr    Th   von  Jurgensen,  of  Tübingen  ;  Prof.  Dr.  U  Krehl, 

of  CreiSd     and  Prof.   Dr.   L.  von  Schrötter,  of  Vienna.     Edited  by 

GEORcfDocK,   M.D.,   Professor  of  Theory  and  Practice  of   Medicine  and 

Clinical  Medicine,  Tulane  University.      Octavo.  848  pages,  illustrated. 

SOLD  SEPARATELY-PER  VOLUME:    CLOTH.  $5.00  NET  ;    HALF  MOROCCO.  $6  00   NET 

Goepp's    State    Board    Questions 

NEW  (2d)  EDITION 
State  Board  Questions  and  Answers.     By  R.  Max  Goepp.  M.D. 
Professor  of  Clinical  Medicine.  Philadelphia  Polyclinic.     Octavo  of  715 
pages  Cloth,  $4-00  net ;  Half  Morocco,  $^.^0  net. 

^''''^to:r,^t:^^t.^^^^  is  so  ..r^r..^,  adapted  as  a  guide  and  self-.ui.  for  those 
intendin?  to  take  State  Board  Exaininations. 


12  SAUNDERS'    BOOKS   ON 

Stevens'  Therapeutics  New  (sth)  Edition 

A  Text-Book  of  Modern  Materia  Medica  and  Therapeutics. 
By  A.  A.  Stevens,  A.  M.,  M.  D.,  Lecturer  on  Physical  Diagnosis  in 
the  University  of  Pennsylvania.     Octavo  of  675  pages.     Cloth,  ^3.50  net. 

Dr.  Stevens'  Therapeutics  is  one  of  the  most  successful  works  on  the 
subject  ever  pubhshed.  In  this  new  edition  the  work  has  undergone  a 
very  thorough  revision,  and  now  represents  the  very  latest  advances. 

The  Medical  Record,  New  York 

"  Among  the  numerous  treatises  on  this  most  important  branch  of  medical  practice, 
this  by  Dr.  Stevens  has  ranked  with  the  best." 

Butler's  Materia  Medica  New  (6th)  Edition 

A  Text-Book  of  Materia  Medica,  Therapeutics,  and  Pharma- 
cology. By  George  F.  Butler,  Ph.  G.,  M.  D.,  Professor  and  Head 
of  the  Department  of  Therapeutics  and  Professor  of  Preventive  and 
Clinical  Medicine,  Chicago  College  of  Medicine  and  Surgery,  Medical 
Department  Valpariso  University.  Octavo  of  702  pages,  illustrated. 
Cloth,  ^4.00  net;  Half  Morocco,  $5.50  net. 

For  this  sixth  edition  Dr.  Butler  has  entirely  remodeled  his  work,  a  great 
part  having  been  rewritten.  All  obsolete  matter  has  been  eliminated,  and 
special  attention  has  been  given  to  the  toxicologic  and  therapeutic  effects 
of  the  newer  compounds. 

Medical  Record,  New  York 

"  Nothing  has  been  omitted  by  the  author  which,  in  his  judgment,  would  add  to  the 
completeness  of  the  text." 

Sollmann's  Pharmacology  New  (zd)  Edition 

A  Text-Book  of  Pharmacology.  By  Torald  Sollmann,  M.  D., 
Professor  of  Pharmacology  and  Materia  Medica,  Western  Reserve  Uni- 
versity.    Octavo  of  1070  pages,  illustrated.     Cloth,  $4.00  net. 

The  author  bases  the  study  of  therapeutics  on  systematic  knowledge  of 
the  nature  and  properties  of  drugs,  and  thus  brings  out  forcibly  the  intimate 
relation  between  pharmacology  and  practical  medicine. 

J.  F.  Fotheringham,  M.  D.,    Trinity  Medical  College,    Toronto. 

"  The  work  certainly  occupies  ground  not  covered  in  so  concise,  useful,  and  scientific  a 
manner  by  any  other  text  I  have  read  on  the  subjects  embraced." 

Amy's  Pharmacy 

Principles  of  Pharmacy.  By  Henry  V.  Arny,  Pk.  G.,  Ph.  D., 
Columbia  University,  New  York.  Octavo  of  11 75  pages,  with  246  illus- 
trations.    Cloth,  ^5.00  net. 

George  Reimann,  Ph.  G.,  Secretary  of  the  New    York  State  Board  of  Pharmacy. 

"  I  would  say  that  the  book  is  certainly  a  great  help  to  the  student,  and  I  think  it  ought 
to  be  in  the  hands  of  every  person  who  is  contemplating  the  study  of  pharmacy." 


THERAPEUTICS  AND  MATERIA  MEDICA  i^ 

*■— ^^-^^— ^  — ■ — _^_^ 

Hinsdale's  Hydrotherapy 

Hydrotherapy :  A  Treatise  on  Hydrotherapy  in  General ;  Its 
Application  to  Special  Affections ;  the  Technic  or  Processes  Employed, 
and  a  Brief  Chapter  on  the  Use  of  Waters  Internally.  By  Guv  Hins- 
dale, M.  D.,  Fellow  Royal  Society  of  Medicine  of  Great  Britain, 
Octavo  of  466  pages,  illustrated.     Cloth,  ^3.50  net. 

INCLUDING  CROUNOTHERAPY 

The  treatment  of  disease  by  hydrotherapeutic  measures  has  assumed  such  an 
important  place  in  medical  practice  that  a  good,  practical  work  on  the  subject 
is  an  essential  in  every  practitioner's  armamentarium.  This  new  work  supplies 
all  needs.  It  describes  fully  the  various  kinds  of  baths,  douches,  sprays  ;  the 
application  of  heat  and  cold  ;  the  internal  use  of  mineral  waters  and  all  otlier 
procedures  included  under  hydrotherapeutic  measures. 

The  Medical  Record 

"  We  cannot  conceive  of  a  work  more  useful  to  the  general  practitioner  than  this,  nor  one 
to  which  he  would  resort  more  frequently  for  reference  and  guidance  in  his  daily  work!" 


Kelly's  Cyclopedia  of  Ameri- 
can Medical  Biog'raphy 

Cyclopedia  of  American  Medical  Biography.  By  Howard  A. 
Kelly,  M.  D.,  Johns  Hopkins  University.  Two  octavos,  averaging  525 
pag^s  each,  with  portraits.  Per  set :  Cloth,  ;^  10.00  net;  Half  Morocco, 
;^  1 3.00  net. 

IN  TWO  VOLUMES 

Dr.  Kelly,  in  these  two  handsome  volumes,  presents  concise,  yet  complete, 
biographies  of  those  men  and  women  who  have  contributed  noteworthily  to  the 
advancement  of  medicine  in  America.  Dr.  Kelly's  reputation  for  painstaking 
care  assures  accuracy  of  statement.  There  are  about  one  thousand  biographies 
included. 


Swan' s  Prescription- writing  and  Formulary 

Prescription-writing  and  Formulary.  By  John  M.  Swan,  M.  D.,  formerly 
Director  Glen  Springs  Sanitarium,  Watkins,  N.  Y.  i6mo  of  185  pages.  Flexible 
leather,  ^^1.25  net. 

Stewart's  Pocket  Therapeutics  and  Dose-book        lX\lfr. 

Pocket  Therapfutics  AND  Dose-Book.  By  Morse  Stewart,  Jr.,  M.D.  32mo 
of  263  pages.     Cloth,  ;gi.oo  net. 


•*/4  SAUNDERS'    BOOKS   ON 

GET  A  •  THE  NEW 

THE  BEST  t\  111  6  11  C  Cl  It  STANDARD 

Illustrated    Dictionary 


New  (6th)  Edition,  Entirely  Reset 

The  American  Illustrated  Medical  Dictionary. — By  W.  A.  New- 

MAN  DoRLAND,  M.  D.,  Editor  of  "The  American  Pocket  Medical  Dic- 
tionary." Large  octavo  of  986  pages,  bound  in  full  flexible  leather. 
Price,  ;^4.50  net;  with  thumb  index,  ^5.00  net, 

KEY  TO  CAPITALIZATION  AND  PRONUNCIATION— ALL  THE  NEW  WORDS 

Howard  A.  'K.eWy ,tA.iy.,  Professor  of  Gyjiecologic  Surgery,  Johns  Hopkins  University. 

"  Dr.  Dorland's  dictionary  is  admirable.     It  is  so  well  gotten  up  and  of  such  convenient 
size.     No  errors  have  been  found  in  my  use  of  it." 


Thornton's  Dose=Book.  New  (4th)  Edition 

Dose-Book  and  Manual  of  Prescription-Writing.  ByE.  Q.  Thornton,  M.D., 
Assistant  Professor  of  Materia  Medica,  Jefferson  Medical  College,  Philadelphia.  Post- 
octavo,  410  pages,  illustrated.     Flexible  leather,  ^2.00  net. 

"  I  will  be  able  to  make  considerable  use  of  that  part  of  its  contents  relating  to  the  correct 
terminology  as  used  in  prescription-writing,  and  it  will  afford  me  much  pleasure  to  recom- 
mend the  book  to  my  classes,  who  often  fail  to  find  this  information  in  their  other  text- 
books."— C.  H.  Miller,  y\..T>.,  Professor  of  Pharmacology ,  Northwestern  University  Medi- 
cal School. 

Lusk    on    Nutrition  New  (2d)  Edition 

Elements  of  the  Science  of  Nutrition.  By  Graham  Lusk,  Ph.  D.,  Professor 
of  Physiology  in  Cornell  University  Medical  School.  Octavo  of  402  pages.  Cloth, 
^3.00  net. 

"  I  shall  recommend  it  highly.  It  is  a  comfort  to  have  such  a  discussion  of  the  subject." 
— Lewellys  F.  Barker,  M.  D.,  Johns  Hopkins  University. 

Camac's  "Epoch-making  Contributions" 

Epoch-making  Contributions  in  Medicine  and  Surgery.  Collected  and 
arranged  by  C.  N.  B.  Camac,  M.  D.,  of  New  York  City.  Octavo  of  450  pages,  illus- 
trated.    Artistically  bound,  ^4.00  net. 

"Dr.  Camac  has  provided  us  with  a  most  interesting  aggregation  of  classical  essays_ 
We  hope  that  members  of  the  profession  will  show  their  appreciation  of  his  endeavors."— 
Therapeutic  Gazette. 


PRACTICE,    MATERIA   MEDICA,   Etc.  15 

The  American  Pocket  Medical  Dictionary  New  (7th)  Edition 

The  American  Pocket  Medical  Dictionary.  Edited  by  W.  A.  Newman  Dor- 
land,  M.  D.,  Editor  "  American  Illustrated  Medical  Dictionary."  610  pages.  Flexible 
leather,  with  gold  eilges,  $1.00  net;   with  thumb  inde.x,  $1.25  net. 

Pusey  and  Caldwell  on  X-Rays  Second  Edition 

The  Pr.\ctical  Application  of  the  Röntgen  Rays  in  Therapeutics  and 
Diagnosis.  By  William  Allen  Pusey,  A.  M.,  M.  D.,  Professor  of  Dermatology  in 
the  University  of  Illinois  ;  and  Eugene  W.  Caldwell,  B.  S.,  Director  of  the  Edward 
N.  Gibbs  X-Ray  Memorial  Laboratory  of  the  University  and  Bellevue  Hospital  Medical 
College,  New  York.  Octavo  of  625  pages,  with  200  illustrations.  Cloth,  ^^5.00  net ; 
Half  Morocco,  $6.50  net. 

Cohen   and   Eshner's   Diag>nOSis.      Second  Revised  Edition 

Essentials  of  Diagnosis.  By  S.  Solis-Cohen,  M.  D.,  Senior  Assistant  Professor 
in  Clinical  Medicine,  Jefferson  Medical  College,  Phila.  ;  and  A.  A.  Eshner,  M.  D., 
Professor  of  Clinical  Medicine,  Philadelphia  I^olyclinic.  Post-octavo,  382  pages  ;  55 
illustrations.      Cloth,  ^l. 00  net.     In  Saunders'  Question-Co})ipend  Series. 

Morris'  Materia  Medica  and  Therapeutics.  New  (7th)  Edition 

Essentials  of  Materia  Medica,  Therapeutics,  and  Prescription-Writing. 
By  Henry  Morris,  M.  D.,  late  Demonstrator  of  Therapeutics,  Jefferson  Medical 
College,  Phila.  Revised  by  W.  A.  Bastedo,  M.  D.,  Instructor  in  Materia  Medica  and 
Pharmacology  at  Columbia  University.  1 2mo,  300  pages.  Cloth,  gl.OO  net.  In  Sounders' 
Question-  Compend  Series. 

Williams'  Practice  of  Medicine 

Essentials  of  the  Practice  of  Medicine.  By  W.  R.  Williams,  M.D., 
formerly  Instructor  in  Medicine  and  Lecturer  on  Hygiene,  Cornell  University  ;  and 
Tutor  in  Therapeutics,  Columbia  U^niversity,  N.  Y.  i2mo  of  456  pages,  illustrated. 
In  Saunders''   Qicestion-Compend  Series.     Double  number,  $1.75  net. 

Todd's  Clinical  Diagnosis  ^^^  ^^^  ^^d)  Edition 

A  Manual  of  Clinical  Diagnosis.  By  James  Campbell  Todd,  M.  D.,  Professor 
of  Pathology,  University  of  Colorado.  l2mo  of  469 pages,  with  164  text-illustrations 
and  10  colored  plates.     Cloth,  $2.25  net. 

Bridge  on  Tuberculosis 

Tuberculosis.  By  Norman  Bridge,  A.  ^L,  ^L  D.,  Emeritus  Professor  of  Medicine 
in  Rush  Medical  College.     i2mo  of  302  pages,  illustrated.     Cloth,  31.50  net. 

Boston's  Clinical  Diagnosis  Second  Edition 

Clinical  Diagnosis.  By  L.  Napoleon  Boston,  M.  D.,  Adjunct  Professor  of  Medi- 
cine and  Director  of  the  Clinical  Laboratories,  Medico-Chirurgical  College,  Philadel- 
phia.     Octavo  of  563  pages,  with  330  illustrations,  many  in  colors.     Cloth,  $4.00  net. 

Arnold's  Medical  Diet  Charts 

Medical  Diet  Charts.  Prepared  by  H.  D.  Arnold,  M.  D.,  Dean  of  Harvard 
Graduate  ^ledical  School.  Boston.  Single  charts,  5  cents;  50  charts,  $2.00  net  ;  500 
charts,  $18.00  net;    1000  charts,  $30.00  net. 

Mathews'  How  to  Succceed  in  Practice 

How  to  Succeed  in  the  Practice  of  Medicine.  By  Joseph  M.  Mathews. 
M.  D.,  LL.D.,  President  American  Medical  Association,  1S98-99.  l2mo  of  215  pages. 
illustrated.     Cloth,  $1.50  net. 


1 6  SAUNDERS'    BOOKS   ON  PRACTICE,  Etc. 

Jakob  and  Eshner's  Internal  Medicine  and  Diagnosis 

Atlas  and  Epitome  of  Internal  Medicine  and  Clinical  Diagnosis.  By  Dr. 
Chr.  Jakob,  of  Erlangen.  Edited,  with  additions,  by  A.  A.  Eshner,  M.  D.,  Pro- 
fessor of  Clinical  Medicine,  Philadelphia  Polyclinic.  With  182  colored  figures  on 
68  plates,  64  text-illustrations,  259  pages  of  text.     Cloth,  ^3.00  net.     In  Saunders^ 

Hand- Atlas  Series. 

Lockwood's  Practice  of  Medicine.  Rj^eTa'-d^Sked 

A  Manual  of  the  Practice  of  Medicine.  By  Geo.  Roe  Lockwood,  M.  D., 
Attending  Physician  to  the  Bellevue  Hospital,  New  York  City.  Octavo,  847  pages, 
with  79  illustrations  in  the  text  and  22  full-page  plates.     Cloth,  $4.00  net. 

Barton  and  Wells*  Medical  Thesaurus 

A  Thesaurus  of  Medical  Words  and  Phrases.  By  W.  M.  Barton,  M.  D.,  and 
W.  A.  Wells,  M.  D.,  of  Georgetown  University,  Washington,  D.  C,  l2mo  of  535 
pages.     Flexible  leather,  ^2.50  net;  thumb  indexed,  ^3.00  net. 

Jelliffe's  Pharmacognosy 

An  Introduction  to  Pharmacognosy.  By  Smith  Ely  Jelliffe,  Ph.  D.,  M.  D.., 
of  Columbia  University.     Octavo,  illustrated.     Cloth,  ^2.50  net. 

Stevens*  Practice  of  Medicine  New  (9th)  Edition 

A  Manual  of  the  Practice  of  Medicine.  By  A.  A.  Stevens,  A.  M.,  M.  D., 
Professor  of  Pathology,  Woman's  Medical  College,  Phila.  Specially  intended  for 
students  preparing  for  graduation  and  hospital  examinations.  Post-octavo,  573  pages, 
illustrated.     Flexible  leather,  #2.50  net. 

Saunders*  Pocket  Formulary  New  (9th)  Edition 

Saunders'  Pocket  Medical  Formulary.  By  William  M.  Powell,  M.  D. 
Containing  183 1  formulas  from  the  best-known  authorities.  With  an  Appendix  con- 
taining Posologic  Table,  Formulas  and  Doses  for  Hypodermic  Medication,  Poisons  and 
their  Antidotes,  Diameters  of  the  Female  Pelvis  and  Fetal  Head,  Obstetrical  Table, 
Diet-list,  Materials  and  Drugs  used  in  Antiseptic  Surgery,  Treatment  of  Asphyxia  from 
Drowning,  Surgical  Remembrancer,  Tables  of  Incompatibles,  Eruptive  Fevers,  etc., 
etc.     In  flexible  leather,  with  side  index,  wallet,  and  flap,  ^1-75  net. 

Gould  and  Pyle's  Curiosities  of  Medicine 

Anomalies  and  Curiosities  of  Medicine.  By  George  M.  Gould,  M.  D.,  and 
Walter  L.  Pyle,  M.  D.  Octavo  of  968  pages,  295  engravings,  and  12  full-page  plates. 
Cloth,  fe.oo  net;  Half  Morocco,  $4.50  net. 

Hatcher  and  Sollmann's  Materia  Medica 

A  Text-Book  of  Materia  Medica  :  including  Laboratory  Exercises  in  the  Histo- 
logic and  Chemie  Examination  of  Drugs.  By  ROBERT  A.  HATCHER,  PH.  G.,  M.  D., 
and  Torald  Sollmann,  M.  D.     i2mo  of  411  pages.     Flexible  leather,  $2.00  net. 

Eichhorst's  Practice  of  Medicine 

A  Text-Book  of  the  Practice  of  Medicine.  By  Dr.  H.  Eichhorst,  Univer- 
sity of  Zurich.  Edited  by  A.  A.  EsHNER,  M.  D.  Two  octavos  of  600  pages  each,  illus- 
trated.    Per  set:  Cloth,  $6.00  net. 


1 

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